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  • The Glycosyltransferase Gene OsUGT90A1 Helps Protect Plasma Membranes During Chilling Stress in Rice
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-24
    Shi Y, Phan H, Liu Y, et al.

    Due to its subtropical origin, rice (Oryza sativa L.) is sensitive to low-temperature stress. We report the identification of LOC_Os04g24110, annotated to encode the UDP-glycosyltransferase enzyme UGT90A1, as a gene associated with the low-temperature seedling survivability (LTSS) quantitative trait locus qLTSS4-1. Haplotype differences in the control region of OsUGT90A1 affecting differential expression in chilling tolerant and chilling sensitive rice accessions rather than differences in protein sequences correlate with chilling tolerance phenotypes. OsUGT90A1 expression is cold regulated, and its overexpression helps to maintain membrane integrity during cold stress and promotes leaf growth during stress recovery, correlating with reduced levels of reactive oxygen species due to increased antioxidant enzyme activities. Overexpression of OsUGT90A1 in Arabidopsis moreover improves freezing survival and salt stress tolerance, correlating with enhanced antioxidant enzyme activities. In rice, overexpression of OsUGT90A1 decreases while gene knockout increases root lengths of three-week-old seedlings, indicating that differential expression of this gene may affect phytohormone activities. Thus, higher OsUGT90A1 expression in chilling tolerant than chilling sensitive accessions helps maintain cell membrane integrity as an abiotic stress tolerance response mechanism to prepare plants to resume growth and development during stress recovery.

    更新日期:2020-01-27
  • Harnessing symbiotic plant–fungus interactions to unleash hidden forces from extreme plant ecosystems
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-24
    Pérez-Alonso M, Guerrero-Galán C, Scholz S, et al.

    The global climate change is arguably one of the biggest threats of our times that already led to a wide range of impacts on the environment, economy, and society. Due to past emissions and the inertia of the climate system, global climate change is estimated to continue for decades even though anthropogenic greenhouse gas emissions could be stopped immediately. In many regions, such as central Europe and the Mediterranean region the temperature is likely to rise by 2–5ºC and annual precipitations are assumed to decrease. Expected heat and drought periods followed by floods, and unpredictable growing seasons are estimated to have detrimental effects on the agricultural production system, causing immense economic losses and problems of food supply.To mitigate the risks provoked by the climate change, agricultural innovations counteracting these effects need to be embraced and accelerated. To achieve maximum improvements, the required agricultural innovations should not focus on the crop side alone, but rather pursue a holistic approach including the entire ecosystem. Over millions of years, plants have evolved in close association with other organisms, in particular with soil microbes that shaped their evolution and contemporary ecology. Many studies already highlighted beneficial interactions among community members, but will it be possible to decipher common molecular pattern and the underlying biochemical framework of interspecies communication? And will we be able to harness the obtained discoveries to improve agricultural performance under environmental stress conditions? In this review, we aim to summarize the current knowledge on plant interactions with fungal endosymbionts found in extreme ecosystems. Special attention will be paid to the interaction of plants with the symbiotic, root-colonizing endophytic fungus Serendipita indica, which has developed to a model system for beneficial plant-fungus interactions.

    更新日期:2020-01-27
  • Role and mechanisms of callose priming in Mycorrhiza-Induced Resistance
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-27
    Sanmartín N, Pastor V, Pastor-Fernández J, et al.

    Mycorrhizal plants (AM) display enhanced resistance to several pathogens. However, the molecular mechanisms regulating Mycorrhiza-Induced Resistance (MIR) are still elusive. We aim to study the mechanisms underlying MIR against Botrytis cinerea and the role of callose accumulation during this process. Mycorrhizal tomato plants inoculated with Rhizoglomus irregularis displayed callose priming upon B. cinereainfection.The callose inhibitor 2-deoxy-D-glucose abolished MIR, confirming the relevance of callose in the bioprotection phenomena. While studying the mechanisms underlying mycorrhiza-induced callose priming, we found that AM plants display an enhanced starch degradation rate that is correlated with the increased levels of β-amylase1 transcripts following pathogen infection. Starch mobilization in AM plants seems coordinated with the increased transcription of sugar transporter and invertase genes. Moreover, the expression levels of genes coding the vesicular trafficking proteins ATL31 and SYP121 and callose synthase PMR4 were higher in the AM plants and further boosted following pathogen infection. These proteins are all key elements in the priming of callose accumulation in Arabidopsis, suggesting that callose priming is an induced resistance mechanism conserved in different plant species. This evidence highlights the importance of sugar mobilization and vesicular trafficking in the priming of callose as a defence mechanism in MIR.

    更新日期:2020-01-27
  • From Element to Development: The power of the essential micronutrient boron to shape morphological processes in plants
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-27
    Matthes M, Robil J, McSteen P.

    Deficiency of the essential nutrient boron (B) in the soil is one of the most widespread micronutrient deficiencies worldwide, leading to developmental defects in root and shoot tissues of plants, and severe yield reductions in many crops. Despite this agricultural importance, the underlying mechanisms of how B shapes plant developmental and morphological processes in detail are still not unequivocally understood. This review evaluates experimental approaches that address our current understanding of how B influences plant morphological processes by focusing on developmental defects observed under B deficiency. We assess what is known about mechanisms that control B homeostasis and specifically highlight; 1) limitations in the methodology that is used to induce B deficiency, 2) differences between mutant phenotypes and normal plants grown under B deficiency, and 3) recent research on analyzing interactions between B and phytohormones. Our analysis highlights the need for standardized methodology to evaluate the roles of B in the cell wall versus other parts of the cell.

    更新日期:2020-01-27
  • Drought stress modulates cuticular wax composition of the grape berry (Vitis vinifera L.)
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-27
    Dimopoulos N, Tindjau R, Wong D, et al.

    Drought events are a major challenge for many horticultural crops, including grapes, which are often cultivated in dry and warm climates. It is not understood how the cuticle contributes to the grape berry response to water deficit (WD), furthermore the cuticular waxes and the related biosynthetic pathways are poorly characterized in this fruit. In this study, we identified candidate wax-related genes from the grapevine genome by phylogenetic and transcriptomic analyses. Developmental and stress-response expression patterns of these candidates were characterized across pre-existing RNA-seq datasets and confirmed a high responsiveness of the pathway to environmental stresses. We then characterized the developmental and WD induced changes in berry cuticular wax composition, and quantified differences in berry transpiration. Cuticular aliphatic wax content was modulated across development and an increase was observed under WD, with wax esters being strongly upregulated. These compositional changes were related to upregulated candidate genes of the aliphatic wax biosynthetic pathway, including CER10, CER2, CER3, CER1, CER4,and WSD1. The effect of WD on berry transpiration was not significant. This study indicates that changes in cuticular wax amount and composition are part of the metabolic response of the grape berry to WD, but these changes do not reduce berry transpiration.

    更新日期:2020-01-27
  • Molecular and genetic bases of heat stress responses in crop plants and breeding for increased resilience and productivity
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-23
    Janni M, Gullì M, Maestri E, et al.

    To ensure the food security of future generations and to address the challenge of the “no hunger zone” proposed by the FAO (Food and Agriculture Organization) crop production must be doubled by 2050, but environmental stresses are counteracting this goal. Heat stress in particular is affecting agricultural crops more frequently and more severely. Since the discovery of the physiological, molecular, and genetic bases of heat stress responses, cultivated plants have become the subject of intense research on how they may avoid or tolerate heat stress by using either natural genetic variation or creating new variation with DNA technologies, mutational breeding, or genome editing. This review reports the current understanding of the genetic and molecular bases of heat stress in crops together with recent approaches to creating heat-tolerant varieties. Research is close to a breakthrough of global relevance, breeding plants fitter to face the biggest challenge of our time.

    更新日期:2020-01-24
  • Leaf hydraulic conductance is linked to leaf symmetry in bifacial, amphistomatic leaves of Sunflower
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-23
    Richardson F, Jordan G, Brodribb T.

    The hydraulic implications of stomatal positioning across leaf surfaces and the impact on internal water flow through amphistomatic leaves are not currently well understood. Amphistomaty potentially provides hydraulic efficiencies if the majority of hydraulic resistance in the leaf exists outside the xylem in the mesophyll. Such a scenario would mean that the same xylem network could equally supply a hypostomatic or amphistomatic leaf. Here we examine leaves of Helianthus annuus to determine whether amphistomaty in this species is associated with higher hydraulic efficiency compared with hypostomatic leaves. We identified asymmetry in the positioning of minor veins which were significantly closer to the abaxial than the adaxial leaf surface combined with lower Kleaf when transpiration was driven through the adaxial rather than abaxial surface. We also identified a degree of coordination in stomatal behaviour driven by leaf hydraulics, where the hydraulic conditions experienced by an individual leaf surface affected the stomatal behaviour on the opposite surface. We found no advantage to amphistomaty based on efficiencies in construction costs of the venous system, represented by vein density:stomatal density, only limited hydraulic independence between leaf surfaces. These results suggest that amphistomaty does not substantially increase whole-leaf hydraulic efficiency.

    更新日期:2020-01-24
  • Signaling pathways underlying nitrogen-dependent changes in root system architecture: from model to crop species
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-23
    Jia Z, Wirén N.

    Among all essential mineral elements, nitrogen (N) is required in largest amounts and thus often a limiting factor for plant growth. Nitrogen is taken up by plant roots in the form of water-soluble nitrate, ammonium and, depending on abundance, low-molecular weight organic N. In soils, the availability and composition of these N forms can vary over space and time, which exposes roots to various local N signals that regulate root system architecture in combination with systemic signals reflecting the N nutritional status of the shoot. Uncovering the molecular mechanisms underlying N-dependent signalling provides great potential to optimize root system architecture for the sake of higher N uptake efficiency in crop breeding. In this review, we summarize prominent signalling mechanisms and their underlying molecular players that derive from external N forms or the internal N nutritional status and modulate root development including root hair formation and gravitropism. The current state of knowledge on these pathways is compared between Arabidopsis and graminaceous plant species.

    更新日期:2020-01-24
  • RETRACTION NOTICE
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-23

    Following concerns expressed by a reader, the Editor-in-Chief and Publisher of Journal of Experimental Botany have taken the decision to retract the following papers. The articles are retracted due to concern over image manipulation and duplication.

    更新日期:2020-01-24
  • Endomembrane architecture and dynamics during secretion of the extracellular matrix of the unicellular charophyte, Penium margaritaceum
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-24
    Domozych D, Sun L, Palacio-Lopez K, et al.

    The extracellular matrix (ECM) of many charophytes, the assemblage of green algae that are the sister group to land plants, is complex, produced in large amounts and has multiple essential functions. An extensive secretory apparatus and endomembrane system are presumably needed to synthesize and secrete the ECM, but structural details of such a system have not been fully characterized. Penium margaritaceum is a valuable unicellular model charophyte for studying secretion dynamics. We report that Penium has a highly organized endomembrane system, consisting of 150-200 non-mobile Golgi bodies that process and package ECM components into different sets of vesicles that traffic to the cortical cytoplasm, where they are transported around the cell by cytoplasmic streaming. At either fixed or transient areas, specific cytoplasmic vesicles fuse with the plasma membrane and secrete their constituents. EPS production was observed to occur in one location of the Golgi body and sometimes in unique Golgi hybrids. Treatment of cells with brefeldin A caused disruption of the Golgi body, inhibition of EPS secretion and cell wall expansion. The structure of the endomembrane system in Penium provides mechanistic insights into how extant charophytes generate large quantities of ECM, which in their ancestors facilitated the colonization of land.

    更新日期:2020-01-24
  • Symplasmic Isolation Marks Cell Fate Changes During Somatic Embryogenesis
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-24
    Godel-Jedrychowska K, Kulinska-Lukaszek K, Horstman A, et al.

    Cell-to-cell signalling is a major mechanism controlling plant morphogenesis. Transport of signalling molecules through plasmodesmata (PD) is one way in which plants promote or restrict intercellular signalling over short distances. PD are membrane lined pores between cells that regulate the intercellular flow of signalling molecules through changes in their size, creating symplasmic fields of connected cells. Here we examined the role of PD and symplasmic communication in the establishment of plant cell totipotency, using somatic embryo induction from Arabidopsis (Arabidopsis thaliana) explants as a model system. Cell-to-cell communication was evaluated using fluorescent tracers, supplemented with histological and ultrastructural analysis, and correlated with expression of a WOX2 embryo reporter. We show that embryogenic cells are isolated symplasmically from non-embryogenic cells regardless of the explant type (immature zygotic embryos or seedlings) and inducer system [2,4-dichlorophenoxyacetic acid (2,4-D) or the BABY BOOM (BBM) transcription factor], but that the symplasmic domains in different explants differ with respect to the maximum size of molecules capable of moving through the PD. Callose deposition in PD preceded WOX2 expression in future sites of somatic embryo development, but later, was greatly reduced in WOX2-expressing domains. Callose deposition was also associated with a decrease DR5 auxin response in embryogenic tissue. Treatment of explants with the callose biosynthesis inhibitor 2-deoxy-D-glucose supressed somatic embryo formation in all three systems studied, and also blocked the observed decrease in DR5expression. Together this data suggests that callose deposition at PD is required for symplasmic isolation and establishment of cell totipotency in Arabidopsis.

    更新日期:2020-01-24
  • Regulation of flowering transition by alternative splicing: the role of the U2 auxiliary factor.
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-13
    Yu-Yi Wang,Feng Xiong,Qiu-Ping Ren,Xiu-Ling Wang

    Flowering transition is regulated by complex genetic networks in response to endogenous and environmental signals. Pre-mRNA splicing is an essential step for the post-transcriptional regulation of gene expression. Alternative splicing of key flowering genes has been investigated in detail over the past decade. However, few splicing factors have been identified as being involved in flowering transition. Human heterodimeric splicing factor U2 snRNP auxiliary factor (U2AF) consists of two subunits, U2AF35 and U2AF65, and functions in 3' splice site recognition in mRNA splicing. Recent studies reveal that Arabidopsis U2AF65a/b and U2AF35a/b play important roles in the splicing of key flowering genes. We summarize recent advances in research on splicing-regulated flowering transition by focusing on the role of Arabidopsis U2AF in the splicing of key flowering-related genes at ambient temperature and in the abscisic acid signaling pathways.

    更新日期:2020-01-24
  • Histone tales: lysine methylation, a protagonist in Arabidopsis development.
    J. Exp. Bot. (IF 5.360) Pub Date : null
    Kai Cheng,Yingchao Xu,Chao Yang,Luc Ouellette,Longjian Niu,Xiaochen Zhou,Liutian Chu,Feng Zhuang,Jin Liu,Hualing Wu,Jean-Benoit Charron,Ming Luo

    Histone methylation plays a fundamental role in the epigenetic regulation of gene expression driven by developmental and environmental cues in plants, including Arabidopsis. Histone methyltransferases and demethylases act as "writers" and "erasers" of methylation at lysine and/or arginine residues of core histones, respectively. A third group of proteins, the "readers", recognize and interpret the methylation marks. Emerging evidences confirm the crucial roles of histone methylation in multiple biological processes throughout plant life cycle. In this review, we summarize the regulatory mechanisms of lysine methylation, especially at histone H3 tails, and focus on the recent advances regarding the roles of lysine methylation in Arabidopsis development, from seed performance to reproductive development, and in callus formation.

    更新日期:2020-01-24
  • Interplay between turgor pressure and plasmodesmata during plant development
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-09-29
    Hernández-Hernández V, Benítez M, Boudaoud A, et al.

    Plasmodesmata traverse cell walls, generating connections between neighboring cells. They allow intercellular movement of molecules such as transcription factors, hormones, and sugars, and thus create a symplasmic continuity within a tissue. One important factor that determines plasmodesmal permeability is their aperture, which is regulated during developmental and physiological processes. Regulation of aperture has been shown to affect developmental events such as vascular differentiation in the root, initiation of lateral roots, or transition to flowering. Extensive research has unraveled molecular factors involved in the regulation of plasmodesmal permeability. Nevertheless, many plant developmental processes appear to involve feedbacks mediated by mechanical forces, raising the question of whether mechanical forces and plasmodesmal permeability affect each other. Here, we review experimental data on how one of these forces, turgor pressure, and plasmodesmal permeability may mutually influence each other during plant development, and we discuss the questions raised by these data. Addressing such questions will improve our knowledge of how cellular patterns emerge during development, shedding light on the evolution of complex multicellular plants.

    更新日期:2020-01-24
  • In silico study of the role of cell growth factors on photosynthesis using a virtual leaf tissue generator coupled to a microscale photosynthesis gas exchange model.
    J. Exp. Bot. (IF 5.360) Pub Date : null
    M A Retta,M K Abera,H N C Berghuijs,P Verboven,P C Struik,B M Nicolaï

    Computational tools that allow in silico analysis of the role of cell growth and division on photosynthesis are scarce. We present a freely available tool that combines a virtual leaf tissue generator and a two-dimensional microscale model of gas transport during C3 photosynthesis. A total of 270 mesophyll geometries were generated with varying degree of growth anisotropy, growth extent and extent of schizogenous airspace formation in the palisade mesophyll. The anatomical properties of the virtual leaf tissue and microscopic cross sections of actual leaf tissue of tomato (Solanum lycopersicum L.) were statistically compared. Model equations for transport of CO2 in the liquid phase of the leaf tissue were discretized over the geometries. The virtual leaf tissue generator produced a leaf anatomy of tomato that was statistically similar to real tomato leaf tissue. The response of photosynthesis to intercellular CO2 predicted by a model that used the virtual leaf tissue geometry compared well with measured values. The results indicate that the light-saturated rate of photosynthesis was influenced by interactive effects of extent and directionality of cell growth and degree of airspace formation through the exposed surface of mesophyll per leaf area. The tool could be used further in investigations of improving photosynthesis and gas exchange in relation to cell growth and leaf anatomy.

    更新日期:2020-01-24
  • The small GTPase Rab5a and its guanine nucleotide exchange factors are involved in post-Golgi trafficking of storage proteins in developing soybean cotyledon
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-16
    Wei Z, Pan T, Zhao Y, et al.

    Storage protein is the most abundant nutritional component in soybean seed. Morphology-based evidence has verified that storage proteins are initially synthesized on the endoplasmic reticulum, and then follow the Golgi-mediated pathway to the protein storage vacuole. However, the molecular mechanisms of storage protein trafficking in soybean remain unknown. Here, we clone the soybean homologs of Rab5 and its guanine nucleotide exchange factor (GEF) VPS9. GEF activity combined with yeast two-hybrid assays demonstrated that GmVPS9a2 might specifically act as the GEF of the canonical Rab5, while GmVPS9b functions as a common activator for all Rab5s. Subcellular localization experiments showed that GmRab5a was dually localized to the trans-Golgi network and pre-vacuolar compartments in developing soybean cotyledon cells. Expression of a dominant negative variant of Rab5a, or RNAi of either Rab5a or GmVPS9s, significantly disrupted trafficking of mRFP–CT10, a cargo marker for storage protein sorting, to protein storage vacuoles in maturing soybean cotyledons. Together, our results systematically revealed the important role of GmRab5a and its GEFs in storage protein trafficking, and verified the transient expression system as an efficient approach for elucidating storage protein trafficking mechanisms in seed.

    更新日期:2020-01-24
  • Redox homeostasis in the growth zone of the rice leaf plays a key role in cold tolerance
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-18
    Gázquez A, Abdelgawad H, Baggerman G, et al.

    We analysed the cellular and molecular changes in the leaf growth zone of tolerant and sensitive rice varieties in response to suboptimal temperatures. Cold reduced the final leaf length by 35% and 51% in tolerant and sensitive varieties, respectively. Tolerant lines exhibited a smaller reduction of the leaf elongation rate and greater compensation by an increased duration of leaf growth. Kinematic analysis showed that cold reduced cell production in the meristem and the expansion rate in the elongation zone, but the latter was compensated for by a doubling of the duration of cell expansion. We performed iTRAQ proteome analysis on proliferating and expanding parts of the leaf growth zone. We identified 559 and 542 proteins, of which 163 and 210 were differentially expressed between zones, and 96 and 68 between treatments, in the tolerant and sensitive lines, respectively. The categories protein biosynthesis and redox homeostasis were significantly overrepresented in the up-regulated proteins. We therefore measured redox metabolites and enzyme activities in the leaf growth zone, demonstrating that tolerance of rice lines to suboptimal temperatures correlates with the ability to up-regulate enzymatic antioxidants in the meristem and non-enzymatic antioxidants in the elongation zone.

    更新日期:2020-01-24
  • AKINβ1, a subunit of SnRK1, regulates organic acid metabolism and acts as a global modulator of genes involved in carbon, lipid, and nitrogen metabolism
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-18
    Wang Y, Wang L, Micallef B, et al.

    The sucrose non-fermenting-1-related protein kinase 1 (SnRK1) is a highly conserved heterotrimeric protein kinase in plants. It possesses a catalytic subunit (α) and two regulatory subunits (β and γ). The effects of altered expression of AKINβ1 on carbohydrate metabolism and gene expression in leaves were investigated in an Arabidopsis T-DNA insertion mutant. The contents of key intermediates in the tricarboxylic acid (TCA) cycle of the mutant leaves were markedly reduced throughout the diurnal cycle, coupled with a decrease in measurable respiration rate. Compared with the wild type, 2485 genes and 188 genes were differentially expressed in leaves of the akinβ1 mutant in response to light and darkness, respectively. Among these, several genes exhibited very substantial decreases in expression. Notably, expression of particular isoforms of multigene families involved in malate and lipid metabolism and nitrate uptake showed decreases of 40- to 240-fold during the light period, but not during darkness. The subcellular localization of AKINβ1 and the regulatory function of N-myristoylation for this localization were investigated, showing that AKINβ1 localizes to the Golgi. A model is hypothesized to explain the effects of AKINβ1 on metabolism and gene expression in Arabidopsis.

    更新日期:2020-01-24
  • Transcription factor CaNAC1 regulates low-temperature-induced phospholipid degradation in green bell pepper
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-18
    Kong X, Zhou Q, Zhou X, et al.

    Phospholipids constitute the main component of biomembranes. During low-temperature storage and transportation of harvested bell peppers (Capsicum annuum), chilling injury participates in their decay. A primary cause of this chilling injury is phospholipid degradation. In this study, three genes encoding phospholipase D (PLD) were identified from bell peppers and their activities were examined under cold stress. Low temperature (4 °C) induced strong accumulation of the CaPLDα4 transcript, suggesting that it is associated with the phenomenon of phospholipid degradation and destruction of cell membranes. Low temperature also significantly induced increased amounts of NAM-ATAF1/2-CUC2 (NAC) domain transcription factors. CaNAC1 was found to interact with the promoter of CaPLD4 in a yeast one-hybrid screen. Electrophoretic mobility shift and ß-glucuronidase reporter assays demonstrated that CaNAC1 binds to the CTGCAG motif in the CaPLDα4 promoter, thereby activating its transcription and controlling phospholipid degradation. The ubiquitination sites of the CaNAC1 protein were characterized by liquid chromatography–tandem mass spectrometry. We conclude that CaNAC1 is a transcriptional activator of CaPLDα4 and suggested that it participates in the degradation of membrane lipids in bell peppers when they are stored at low temperature.

    更新日期:2020-01-24
  • Robust non-syntenic gene expression patterns in diverse maize hybrids during root development
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-22
    Baldauf J, Vedder L, Schoof H, et al.

    Distantly related maize (Zea mays L.) inbred lines exhibit an exceptional degree of structural genomic diversity, which is probably unique among plants. This study systematically investigated the developmental and genotype-dependent regulation of the primary root transcriptomes of a genetically diverse panel of maize F1-hybrids and their parental inbred lines. While we observed substantial transcriptomic changes during primary root development, we demonstrated that hybrid-associated gene expression patterns, including differential, non-additive, and allele-specific transcriptome profiles, are particularly robust to these developmental fluctuations. For instance, differentially expressed genes with preferential expression in hybrids were highly conserved during development in comparison to their parental counterparts. Similarly, in hybrids a major proportion of non-additively expressed genes with expression levels between the parental values were particularly conserved during development. Importantly, in these expression patterns non-syntenic genes that evolved after the separation of the maize and sorghum lineages were systemically enriched. Furthermore, non-syntenic genes were substantially linked to the conservation of all surveyed gene expression patterns during primary root development. Among all F1-hybrids, between ~40% of the non-syntenic genes with unexpected allelic expression ratios and ~60% of the non-syntenic differentially and non-additively expressed genes were conserved and therefore robust to developmental changes. Hence, the enrichment of non-syntenic genes during primary root development might be involved in the developmental adaptation of maize roots and thus the superior performance of hybrids.

    更新日期:2020-01-24
  • Submergence stress-induced hypocotyl elongation through ethylene signaling-mediated regulation of cortical microtubules in Arabidopsis
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-22
    Wang X, Ma Q, Wang R, et al.

    Plant growth is significantly altered in response to submergence stress. However, the molecular mechanisms used by seedlings in response to this stress, especially for hypocotyl growth, are largely unknown in terrestrial plants such as Arabidopsis thaliana. The microtubule cytoskeleton participates in plant cell growth, but it remains unclear whether submergence-mediated plant growth involves the microtubule cytoskeleton. We demonstrated that in Arabidopsis submergence induced underwater hypocotyl elongation through the activation of ethylene signaling, which modulated cortical microtubule reorganization. Submergence enhanced ethylene signaling, which then activated and stabilized its downstream transcription factor, phytochrome-interacting factor 3 (PIF3), to promote hypocotyl elongation. In particular, the regulation of microtubule organization was important for this physiological process. Microtubule-destabilizing protein 60 (MDP60), which was previously identified as a downstream effector of PIF3, played a positive role in submergence-induced hypocotyl elongation. Submergence induced MDP60 expression through ethylene signaling. The effects of submergence on hypocotyl elongation and cortical microtubule reorganization were suppressed in mdp60 mutants. These data suggest a potential mechanism by which submergence activates ethylene signaling to promote underwater hypocotyl elongation via alteration of the microtubule cytoskeleton in Arabidopsis.

    更新日期:2020-01-24
  • Diverse trajectories of plastome degradation in holoparasitic Cistanche and genomic location of the lost plastid genes
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-23
    Liu X, Fu W, Tang Y, et al.

    The plastid genomes (plastomes) of non-photosynthetic plants generally undergo gene loss and pseudogenization. Despite massive plastomes reported in different parasitism types of the broomrape family (Orobanchaceae), more plastomes representing different degradation patterns in a single genus are expected to be explored. Here, we sequence and assemble the complete plastomes of three holoparasitic Cistanche species (C. salsa, C. mongolica, and C. sinensis) and compare them with the available plastomes of Orobanchaceae. We identified that the diverse degradation trajectories under purifying selection existed among three Cistanche clades, showing obvious size differences in the entire plastome, long single copy region, and non-coding region, and different patterns of the retention/loss of functional genes. With few exceptions of putatively functional genes, massive plastid fragments, which have been lost and transferred into the mitochondrial or nuclear genomes, are non-functional. In contrast to the equivalents of the Orobanche species, some plastid-derived genes with diverse genomic locations are found in Cistanche. The early and initially diverged clades in different genera such as Cistanche and Aphyllon possess obvious patterns of plastome degradation, suggesting that such key lineages should be considered prior to comparative analysis of plastome evolution, especially in the same genus.

    更新日期:2020-01-24
  • Sigma factor 1 in chloroplast gene transcription and photosynthetic light acclimation
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-23
    Macadlo L, Ibrahim I, Puthiyaveetil S, et al.

    Sigma factors are dissociable subunits of bacterial RNA polymerase that ensure efficient transcription initiation from gene promoters. Owing to their prokaryotic origin, chloroplasts possess a typical bacterial RNA polymerase together with its sigma factor subunit. The higher plant Arabidopsis thaliana contain as many as six sigma factors for the hundred or so of its chloroplast genes. The role of this relatively large number of transcription initiation factors for the miniature chloroplast genome, however, is not fully understood. Using two Arabidopsis T-DNA insertion mutants, we show that sigma factor 1 (SIG1) initiates transcription of a specific subset of chloroplast genes. We further show that the photosynthetic control of PSI reaction center gene transcription requires complementary regulation of the nuclear SIG1 gene at the transcriptional level. This SIG1 gene regulation is dependent on both a plastid redox signal and a light signal transduced by the phytochrome photoreceptor.

    更新日期:2020-01-24
  • CIRCADIAN CLOCK ASSOCIATED 1 and ATAF2 differentially suppress cytochrome P450-mediated brassinosteroid inactivation
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-23
    Peng H, Neff M, Napier R.

    Brassinosteroids (BRs) are a group of steroid hormones regulating plant growth and development. Since BRs do not undergo transport among plant tissues, their metabolism is tightly regulated by transcription factors (TFs) and feedback loops. BAS1 (CYP734A1, formerly CYP72B1) and SOB7 (CYP72C1) are two BR-inactivating cytochrome P450s identified in Arabidopsis thaliana. We previously found that a TF ATAF2 (ANAC081) suppresses BAS1 and SOB7 expression by binding to the Evening Element (EE) and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1)-binding site (CBS) on their promoters. Both the EE and CBS are known binding targets of the circadian regulatory protein CCA1. Here, we confirm that CCA1 binds the EE and CBS motifs on BAS1 and SOB7 promoters, respectively. Elevated accumulations of BAS1 and SOB7 transcripts in the CCA1 null mutant cca1-1 indicate that CCA1 is a repressor of their expression. When compared with either cca1-1 or the ATAF2 null mutant ataf2-2, the cca1-1 ataf2-2 double mutant shows higher SOB7 transcript accumulations and a stronger BR-insensitive phenotype of hypocotyl elongation in white light. CCA1 interacts with ATAF2 at both DNA–protein and protein–protein levels. ATAF2, BAS1, and SOB7 are all circadian regulated with distinct expression patterns. These results demonstrate that CCA1 and ATAF2 differentially suppress BAS1- and SOB7-mediated BR inactivation.

    更新日期:2020-01-24
  • Brassinosteroids act as a positive regulator of NBR1-dependent selective autophagy in response to chilling stress in tomato
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-23
    Chi C, Li X, Fang P, et al.

    Autophagy is a highly conserved and regulated catabolic process involved in the degradation of protein aggregates, which plays critical roles in eukaryotes. In plants, multiple molecular processes can induce or suppress autophagy but the mechanism of its regulation by phytohormones is poorly understood. Brassinosteroids (BRs) are steroid phytohormones that play crucial roles in plant response to stresses. Here, we investigate the role of BRs in NBR1-dependent selective autophagy in response to chilling stress in tomato. BRs and their signaling element BZR1 can induce autophagy and accumulation of the selective autophagy receptor NBR1 in tomato under chilling stress. Cold increased the stability of BZR1, which was promoted by BRs. Cold- and BR-induced increased BZR1 stability activated the transcription of several autophagy-related genes (ATGs) and NBR1 genes by directly binding to their promoters, which resulted in selective autophagy. Furthermore, silencing of these ATGs or NBR1 genes resulted in a decreased accumulation of several functional proteins and an increased accumulation of ubiquitinated proteins, subsequently compromising BR-induced cold tolerance. These results strongly suggest that BRs regulate NBR1-dependent selective autophagy in a BZR1-dependent manner in response to chilling stress in tomato.

    更新日期:2020-01-24
  • Combining phenotype, genotype, and environment to uncover genetic components underlying water use efficiency in Persian walnut
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-23
    Arab M, Marrano A, Abdollahi-Arpanahi R, et al.

    Walnut production is challenged by climate change and abiotic stresses. Elucidating the genomic basis of adaptation to climate is essential to breeding drought-tolerant cultivars for enhanced productivity in arid and semi-arid regions. Here, we aimed to identify loci potentially involved in water use efficiency (WUE) and adaptation to drought in Persian walnut using a diverse panel of 95 walnut families (950 seedlings) from Iran, which show contrasting levels of water availability in their native habitats. We analyzed associations between phenotypic, genotypic, and environmental variables from data sets of 609 000 high-quality single nucleotide polymorphisms (SNPs), three categories of phenotypic traits [WUE-related traits under drought, their drought stress index, and principal components (PCs)], and 21 climate variables and their combination (first three PCs). Our genotype–phenotype analysis identified 22 significant and 266 suggestive associations, some of which were for multiple traits, suggesting their correlation and a possible common genetic control. Also, genotype–environment association analysis found 115 significant and 265 suggestive SNP loci that displayed potential signals of local adaptation. Several sets of stress-responsive genes were found in the genomic regions significantly associated with the aforementioned traits. Most of the candidate genes identified are involved in abscisic acid signaling, stomatal regulation, transduction of environmental signals, antioxidant defense system, osmotic adjustment, and leaf growth and development. Upon validation, the marker–trait associations identified for drought tolerance-related traits would allow the selection and development of new walnut rootstocks or scion cultivars with superior WUE.

    更新日期:2020-01-24
  • WRKY44 represses expression of the wound-induced sesquiterpene biosynthetic gene ASS1 in Aquilaria sinensis
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-23
    Sun P, Xu Y, Yu C, et al.

    Agarwood is derived from wounds in Aquilaria trees and is widely used in traditional medicine, incense, and perfume. Sesquiterpenes are one of the main active components in agarwood and are known to be induced by wounding or injury; However, the molecular mechanisms by which wounding leads to sesquiterpene formation remain largely unknown. Agarwood sesquiterpene synthase 1 (ASS1) is one of key enzymes responsible for the biosynthesis of sesquiterpenes and is a crucial jasmonate (JA)-responsive wound-inducible synthase. However, it is not known why ASS1 is not expressed in healthy trees and how its expression is induced as a result of wounding. Here, we report that ASS1 is a wound-induced gene with a promoter in which a 242-bp region (–973 to –731bp) is identified as the core sequence for responding to wound signals. AsWRKY44 binds directly to this region and represses ASS1 promoter activity. Down-regulation or disruption of AsWRKY44 can relieve the inhibition and activate ASS1 expression. In addition, AsWRKY44 is degraded and the expression of ASS1 is significantly up-regulated in response to exogenous application of methyl jasmonate. Thus, AsWRKY44 is a crucial negative regulator of wound-induced ASS1 transcription, and is central to the mechanism of sesquiterpene biosynthesis in agarwood.

    更新日期:2020-01-24
  • Single-base resolution methylome of cotton cytoplasmic male sterility system reveals epigenomic changes in response to high-temperature stress during anther development
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-23
    Zhang M, Zhang X, Guo L, et al.

    Anther development in flowering plants is highly sensitive to high-temperature (HT) stress. Understanding the potential epigenetic mechanism of anther infertility induced by HT stress in cotton (Gossypium hirsutum L.) is crucial for the effective use of genetic resources to guide plant breeding. Using the whole-genome bisulfite sequencing, we map cytosine methylation at single-base resolution across the whole genome of cotton anthers, and changes in the methylome of the cytoplasmic male sterility system associated with HT stress were analysed in two cotton lines with contrasting HT stress tolerance. The cotton anther genome was found to display approximately 31.6%, 68.7%, 61.8%, and 21.8% methylation across all sequenced C sites and in the CG, CHG, and CHH sequence contexts, respectively. In an integrated global methylome and transcriptome analysis, only promoter-unmethylated genes showed higher expression levels than promoter-methylated genes, whereas gene body methylation presented an obvious positive correlation with gene expression. The methylation profiles of transposable elements in cotton anthers were characterized, and more differentially methylated transposable elements were demethylated under HT stress. HT-induced promoter methylation changes led to the up-regulation of the mitochondrial respiratory chain enzyme-associated genes GhNDUS7, GhCOX6A, GhCX5B2, and GhATPBM, ultimately promoting a series of redox processes to form ATP for normal anther development under HT stress. In vitro application of the common DNA methylation inhibitor 5-azacytidine and accelerator methyl trifluoromethanesulfonate demonstrated that DNA demethylation promoted anther development, while increased methylation only partially inhibited anther development under HT stress.

    更新日期:2020-01-24
  • Arabidopsis thaliana SEED DORMANCY 4-LIKE regulates dormancy and germination by mediating the gibberellin pathway
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-23
    Cao H, Han Y, Li J, et al.

    The molecular mechanisms underlying seed dormancy and germination are not fully understood. Here, we show that Arabidopsis thaliana SEED DORMANCY 4-LIKE (AtSdr4L) is a novel specific regulator of dormancy and germination. AtSdr4L encodes a protein with an unknown biochemical function that is localized in the nucleus and is expressed specifically in seeds. Loss of function of AtSdr4L results in increased seed dormancy. The germination of freshly harvested seeds of the Atsdr4l mutant is insensitive to gibberellin (GA). After-ripened mutant seeds are hypersensitive to the GA biosynthesis-inhibitor paclobutrazol but show unaltered sensitivity to abscisic acid. Several GA biosynthesis genes and GA-regulated cell wall remodeling genes are down-regulated in the mutant in both dormant and after-ripened seeds. These results suggest that the Atsdr4l mutation causes both decreased GA biosynthesis and reduced responses. In addition, a genetic analysis indicated that AtSdr4L is epistatic to DELAY OF GERMINATION1 (DOG1) for dormancy and acts upstream of RGA-LIKE 2 (RGL2) in the GA pathway. We propose that AtSdr4L regulates seed dormancy and germination by mediating both the DOG1 and GA pathways.

    更新日期:2020-01-24
  • Positive root pressure is critical for whole-plant desiccation recovery in two species of terrestrial resurrection ferns
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-23
    Holmlund H, Davis S, Ewers F, et al.

    Desiccation-tolerant (DT) organisms can lose nearly all their water without dying. Desiccation tolerance allows organisms to survive in a nearly completely dehydrated, dormant state. At the cellular level, sugars and proteins stabilize cellular components and protect them from oxidative damage. However, there are few studies of the dynamics and drivers of whole-plant recovery in vascular DT plants. In vascular DT plants, whole-plant desiccation recovery (resurrection) depends not only on cellular rehydration, but also on the recovery of organs with unequal access to water. In this study, in situ natural and artificial irrigation experiments revealed the dynamics of desiccation recovery in two DT fern species. Organ-specific irrigation experiments revealed that the entire plant resurrected when water was supplied to roots, but leaf hydration alone (foliar water uptake) was insufficient to rehydrate the stele and roots. In both species, pressure applied to petioles of excised desiccated fronds resurrected distal leaf tissue, while capillarity alone was insufficient to resurrect distal pinnules. Upon rehydration, sucrose levels in the rhizome and stele dropped dramatically as starch levels rose, consistent with the role of accumulated sucrose as a desiccation protectant. These findings provide insight into traits that facilitate desiccation recovery in dryland ferns associated with chaparral vegetation of southern California.

    更新日期:2020-01-24
  • Analysis of potential redundancy among Arabidopsis 6-phosphogluconolactonase isoforms in peroxisomes
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-23
    Lansing H, Doering L, Fischer K, et al.

    Recent work revealed that PGD2, an Arabidopsis 6-phosphogluconate dehydrogenase (6-PGD) catalysing the third step of the oxidative pentose-phosphate pathway (OPPP) in peroxisomes, is essential during fertilization. Earlier studies on the second step, catalysed by PGL3, a dually targeted Arabidopsis 6-phosphogluconolactonase (6-PGL), reported the importance of OPPP reactions in plastids but their irrelevance in peroxisomes. Assuming redundancy of 6-PGL activity in peroxisomes, we examined the sequences of other higher plant enzymes. In tomato, there exist two 6-PGL isoforms with the strong PTS1 motif SKL. However, their analysis revealed problems regarding peroxisomal targeting: reporter–PGL detection in peroxisomes required construct modification, which was also applied to the Arabidopsis isoforms. The relative contribution of PGL3 versus PGL5 during fertilization was assessed by mutant crosses. Reduced transmission ratios were found for pgl3-1 (T-DNA-eliminated PTS1) and also for knock-out allele pgl5-2. The prominent role of PGL3 showed as compromised growth of pgl3-1 seedlings on sucrose and higher activity of mutant PGL3-1 versus PGL5 using purified recombinant proteins. Evidence for PTS1-independent uptake was found for PGL3-1 and other Arabidopsis PGL isoforms, indicating that peroxisome import may be supported by a piggybacking mechanism. Thus, multiple redundancy at the level of the second OPPP step in peroxisomes explains the occurrence of pgl3-1 mutant plants.

    更新日期:2020-01-24
  • Xylem embolism in leaves does not occur with open stomata: evidence from direct observations using the optical visualization technique
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-23
    Creek D, Lamarque L, Torres-Ruiz J, et al.

    Drought represents a major abiotic constraint to plant growth and survival. On the one hand, plants keep stomata open for efficient carbon assimilation while, on the other hand, they close them to prevent permanent hydraulic impairment from xylem embolism. The order of occurrence of these two processes (stomatal closure and the onset of leaf embolism) during plant dehydration has remained controversial, largely due to methodological limitations. However, the newly developed optical visualization method now allows concurrent monitoring of stomatal behaviour and leaf embolism formation in intact plants. We used this new approach directly by dehydrating intact saplings of three contrasting tree species and indirectly by conducting a literature survey across a greater range of plant taxa. Our results indicate that increasing water stress generates the onset of leaf embolism consistently after stomatal closure, and that the lag time between these processes (i.e. the safety margin) rises with increasing embolism resistance. This suggests that during water stress, embolism-mediated declines in leaf hydraulic conductivity are unlikely to act as a signal for stomatal down-regulation. Instead, these species converge towards a strategy of closing stomata early to prevent water loss and delay catastrophic xylem dysfunction.

    更新日期:2020-01-24
  • miR156-targeted SPL10 controls Arabidopsis root meristem activity and root-derived de novo shoot regeneration via cytokinin responses
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-23
    Barrera-Rojas C, Rocha G, Polverari L, et al.

    Root growth is modulated by different factors, including phytohormones, transcription factors, and microRNAs (miRNAs). MicroRNA156 and its targets, the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes, define an age-dependent pathway that controls several developmental processes, including lateral root emergence. However, it remains unclear whether miR156-regulated SPLs control root meristem activity and root-derived de novo shoot regeneration. Here, we show that MIR156 and SPL genes have opposing expression patterns during the progression of primary root (PR) growth in Arabidopsis, suggesting that age cues may modulate root development. Plants with high miR156 levels display reduced meristem size, resulting in shorter primary root (PRs). Conversely, plants with reduced miR156 levels show higher meristem activity. Importantly, loss of function of SPL10 decreases meristem activity, while SPL10 de-repression increases it. Meristem activity is regulated by SPL10 probably through the reduction of cytokinin responses, via the modulation of type-B ARABIDOPSIS RESPONSE REGULATOR1(ARR1) expression. We also show that SPL10 de-repression in the PRs abolishes de novo shoot regenerative capacity by attenuating cytokinin responses. Our results reveal a cooperative regulation of root meristem activity and root-derived de novo shoot regeneration by integrating age cues with cytokinin responses via miR156-targeted SPL10.

    更新日期:2020-01-24
  • Time-gated confocal microscopy reveals accumulation of exocyst subunits at the plant–pathogen interface
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-26
    Overdijk E, Tang H, Borst J, et al.

    Polarized exocytosis is essential for plant development and defence. The exocyst, an octameric protein complex that tethers exocytotic vesicles to the plasma membrane, targets exocytosis. Upon pathogen attack, secreted materials form papillae to halt pathogen penetration. To determine if the exocyst is directly involved in targeting exocytosis to infection sites, information about its localization is instrumental. Here, we investigated exocyst subunit localization in the moss Physcomitrella patens upon pathogen attack and infection by Phytophthora capsici. Time-gated confocal microscopy was used to eliminate autofluorescence of deposited material around infection sites, allowing the visualization of the subcellular localization of exocyst subunits and of v-SNARE Vamp72A1-labelled exocytotic vesicles during infection. This showed that exocyst subunits Sec3a, Sec5b, Sec5d, and Sec6 accumulated at sites of attempted pathogen penetration. Upon pathogen invasion, the exocyst subunits accumulated on the membrane surrounding papilla-like structures and hyphal encasements. Vamp72A1-labelled vesicles were found to localize in the cytoplasm around infection sites. The re-localization of exocyst subunits to infection sites suggests that the exocyst is directly involved in facilitating polarized exocytosis during pathogenesis.

    更新日期:2020-01-24
  • Dodder-transmitted mobile signals prime host plants for enhanced salt tolerance
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-26
    Li S, Zhang J, Liu H, et al.

    The dodders (Cuscuta spp.) are a genus of shoot parasites. In nature, a dodder often simultaneously parasitizes two or more neighboring hosts. Salt stress is a common abiotic stress for plants. It is unclear whether dodder transmits physiologically relevant salt stress-induced systemic signals among its hosts and whether these systemic signals affect the hosts’ tolerance to salt stress. Here, we simultaneously parasitized two or more cucumber plants with dodder. We found that salt treatment of one host highly primed the connected host, which showed strong decreases in the extent of leaf withering and cell death in response to subsequent salt stress. Transcriptomic analysis indicated that 24 h after salt treatment of one cucumber, the transcriptome of the other dodder-connected cucumber largely resembled that of the salt-treated one, indicating that inter-plant systemic signals primed these dodder-connected cucumbers at least partly through transcriptomic reconfiguration. Furthermore, salt treatment of one of the cucumbers induced physiological changes, including altered proline contents, stomatal conductance, and photosynthetic rates, in both of the dodder-connected cucumbers. This study reveals a role of dodder in mediating salt-induced inter-plant signaling among dodder-connected hosts and highlights the physiological function of these mobile signals in plant–plant interactions under salt stress.

    更新日期:2020-01-24
  • PAMP-INDUCED SECRETED PEPTIDE 3 modulates immunity in Arabidopsis
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-28
    Najafi J, Brembu T, Vie A, et al.

    Small post-translationally modified peptides are important signalling components of plant defence responses against phytopathogens, acting as both positive and negative modulators. PAMP-INDUCED SECRETED PEPTIDE (PIP) 1 and 2 have been shown to amplify plant immunity. Here we investigate the role of the related peptide PIP3 in the regulation of immune response in Arabidopsis. Treatment with synthetic PIP peptides led to similar transcriptome reprogramming, indicating an effect on innate immunity-related processes and phytohormones, including jasmonic acid (JA) biosynthesis and signalling. PIP3 overexpressing (OX) plants showed enhanced growth inhibition in response to flg22 exposure. In addition, flg22-induced production of reactive oxygen species and callose deposition was significantly reduced in PIP3-OX plants. Interestingly, PIP3-OX plants showed increased susceptibility toward both Botrytis cinerea and the biotrophic pathogen Pseudomonas syringae. Expression of both JA and salicylic acid (SA) biosynthesis and signalling genes was more induced during B. cinerea infection in PIP3-OX plants compared with wild-type plants. Promoter and ChIP-seq analyses indicated that the transcription factors WRKY18, WRKY33, and WRKY40 cooperatively act as repressors for PIP3. The results point to a fine-tuning role for PIP3 in modulation of immunity through the regulation of SA and JA biosynthesis and signalling pathways in Arabidopsis.

    更新日期:2020-01-24
  • Photoperiod-sensitivity genes (Ppd-1): quantifying their effect on the photoperiod response model in wheat
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-28
    Pérez-Gianmarco T, Severini A, González F, et al.

    Coupling anthesis date to the most suitable environmental conditions is critical for wheat (Triticum aestivum L.) adaptation and yield potential. Development to anthesis is controlled by temperature and photoperiod. Response to photoperiod is chiefly modulated by Ppd-1 genes, but their effect on the quantitative response to photoperiod of (i) time to anthesis and (ii) pre-anthesis phases remains largely unknown. A photoperiod-sensitive spring cultivar, Paragon, and near-isogenic lines of it carrying different combinations of Ppd-1a insensitivity alleles were tested under a wide range of photoperiods, including switches in photoperiod at the onset of stem elongation. Using multimodel inference we found that Ppd-1a alleles reduced photoperiod sensitivity of (i) emergence to anthesis and (ii) emergence to onset of stem elongation, both in a less than additive manner, while threshold photoperiod and intrinsic earliness were unaffected. Sensitivity to current photoperiod from onset of stem elongation to flag leaf and from then to anthesis was milder than for previous phases and was not related to variability in Ppd-1. However, ‘memory’ effects of previously experienced photoperiod on the duration from onset of stem elongation to flag leaf were related to variability in Ppd-1. The characterization and quantification provided here of the effects on development of Ppd-1 allelic combinations should help increase accuracy of genotype-to-phenotype models in predicting wheat phenology.

    更新日期:2020-01-24
  • Flowering time and the identification of floral marker genes in Solanum tuberosum ssp. andigena
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-10-28
    Seibert T, Abel C, Wahl V, et al.

    Solanaceae is a family of flowering plants that includes agricultural species such as tomato (Solanum lycopersicum), eggplant (S. melongena), pepper (Capsicum annuum), and potato (S. tuberosum). The transition from the vegetative to reproductive stage has been extensively investigated in tomato as it affects fruit yield. While potato has mainly been studied with regards to the formation of storage organs, control of flowering time is a subject of increasing interest as development of true seeds is becoming more important for future breeding strategies. Here, we describe a robust growth regime for synchronized development of S. tuberosum ssp. andigena. Using SEM to analyse the developmental stages of the shoot apical meristem (SAM) throughout the floral transition, we show that andigena is a facultative long-day plant with respect to flowering. In addition, we identify the flower meristem identity gene MACROCALYX (StMC) as a marker to distinguish between the vegetative and reproductive stages. We show that the expression of WUSCHEL HOMEOBOX 9 (StWOX9) and ANANTHA (StAN) are specific to the inflorescence meristem and flower meristems in the cyme, respectively. The expression patterns of homologs of Arabidopsis flowering-time regulators were studied, and indicated that SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (StSOC1) and StFD might regulate flowering similar to other plant species.

    更新日期:2020-01-24
  • Sugar sensing responses to low and high light in leaves of the C4 model grass Setaria viridis.
    J. Exp. Bot. (IF 5.360) Pub Date : null
    Clémence Henry,Alexander Watson-Lazowski,Maria Oszvald,Cara Griffiths,Matthew J Paul,Robert T Furbank,Oula Ghannoum

    Although sugar regulate photosynthesis, the signalling pathways underlying this process remain elusive, especially for C4 crops. To address this knowledge gap and identify potential candidate genes, we treated Setaria viridis (C4 model) plants acclimated to medium light intensity (ML, 500 µmol m-2 s-1) with low (LL, 50 µmol m-2 s-1) or high (HL, 1000 µmol m-2 s-1) light for 4 days and observed the consequences on carbon metabolism and the transcriptome of source leaves. LL impaired photosynthesis and reduced leaf content of signalling sugars (glucose, sucrose and trehalose-6-phosphate). Contrastingly, HL strongly induced sugar accumulation without repressing photosynthesis. LL more profoundly impacted leaf transcriptome, including photosynthetic genes. LL and HL contrastingly altered the expression of HXK and SnRK1 sugar sensors and trehalose pathway genes. The expression of key target genes of HXK and SnRK1 were affected by LL and sugar depletion, while surprisingly HL and strong sugar accumulation only slightly repressed the SnRK1 signalling pathway. In conclusion, we demonstrate that LL profoundly impacted photosynthesis and the transcriptome of S. viridis source leaves, while HL altered sugar levels more than LL. We also present the first evidence that sugar signalling pathways in C4 source leaves may respond to light intensity and sugar accumulation differently to C3 source leaves.

    更新日期:2020-01-24
  • CYP71D8L is a key regulator involved in growth and stress responses by mediating gibberellin homeostasis in rice
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-11-03
    Zhou J, Li Z, Xiao G, et al.

    Phytohormones are crucial in the regulation of plant growth and development, and in responses to adverse environments. Multiple cytochrome P450 monooxygenases (CYP450s) are involved in the biosynthesis and catabolism of phytohormones. Here, we report that a CYP450 member of the CYP71 clan in rice, OsCYP71D8L, participates in the control of multiple agronomic traits and abiotic stress responses by affecting gibberellin (GA) and cytokinin (CK) homeostasis. The gain-of-function mutant cyp71d8l and transgenic plants overexpressing CYP71D8L (CYP71D8L-OE) display similar phenotypes compared to the wild-type (WT), including dwarfed plants, reduced panicle length, reduced grain number per panicle, and decreased levels of endogenous GAs. Moreover, the dwarfed plant trait and the less-developed roots of CYP71D8L-OE and cyp71d8l seedlings could be rescued by application of GA3 or the CK biosynthetic inhibitor lovastatin, and exacerbated by application of the synthetic CK 6-BA. Importantly, CYP71D8L-OE and cyp71d8l seedlings maintained high chlorophyll contents and low levels of reactive oxygen species, and showed enhanced tolerance to drought and salt stress compared with the WT. Thus, our results suggest that OsCYP71D8L plays important roles in regulating rice growth and stress responses by coordinating the homeostasis of GAs and CKs, and it may therefore be a useful target for engineering stress-tolerant rice varieties.

    更新日期:2020-01-24
  • Hsp70 plays a role in programmed cell death during the remodelling of leaves of the lace plant (Aponogeton madagascariensis)
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-11-06
    Rowarth N, Dauphinee A, Denbigh G, et al.

    Lace plant leaves utilize programmed cell death (PCD) to form perforations during development. The role of heat shock proteins (Hsps) in PCD during lace plant leaf development is currently unknown. Hsp70 amounts were measured throughout lace plant leaf development, and the results indicate that it is highest before and during PCD. Increased Hsp70 amounts correlate with raised anthocyanin content and caspase-like protease (CLP) activity. To investigate the effects of Hsp70 on leaf development, whole plants were treated with either of the known regulators of PCD [reactive oxygen species (ROS) or antioxidants] or an Hsp70 inhibitor, chlorophenylethynylsulfonamide (PES-Cl). ROS treatment significantly increased Hsp70 2-fold and CLP activity in early developing leaves, but no change in anthocyanin and the number of perforations formed was observed. Antioxidant treatment significantly decreased Hsp70, anthocyanin, and CLP activity in early leaves, resulting in the fewest perforations. PES-Cl (25 μM) treatment significantly increased Hsp70 4-fold in early leaves, while anthocyanin, superoxide, and CLP activity significantly declined, leading to fewer perforations. Results show that significantly increased (4-fold) or decreased Hsp70 amounts lead to lower anthocyanin and CLP activity, inhibiting PCD induction. Our data support the hypothesis that Hsp70 plays a role in regulating PCD at a threshold in lace plant leaf development.Hsp70 affects anthocyanin content and caspase-like protease activity, and helps regulate PCD during the remodelling of leaves of lace plant, Aponogeton madagascariensis.

    更新日期:2020-01-24
  • Effect of epistasis and environment on flowering time in barley reveals a novel flowering-delaying QTL allele
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-11-28
    Afsharyan N, Sannemann W, Léon J, et al.

    Flowering time is a complex trait and has a key role in crop yield and adaptation to environmental stressors such as heat and drought. This study aimed to better understand the interconnected dynamics of epistasis and environment and look for novel regulators. We investigated 534 spring barley MAGIC DH lines for flowering time at various environments. Analysis of quantitative trait loci (QTLs), epistatic interactions, QTL × environment (Q×E) interactions, and epistasis × environment (E×E) interactions were performed with single SNP and haplotype approaches. In total, 18 QTLs and 2420 epistatic interactions were detected, including intervals harboring major genes such as Ppd-H1, Vrn-H1, Vrn-H3, and denso/sdw1. Epistatic interactions found in field and semi-controlled conditions were distinctive. Q×E and E×E interactions revealed that temperature influenced flowering time by triggering different interactions between known and newly detected regulators. A novel flowering-delaying QTL allele was identified on chromosome 1H (named ‘HvHeading’) and was shown to be engaged in epistatic and environment interactions. Results suggest that investigating epistasis, environment, and their interactions, rather than only single QTLs, is an effective approach for detecting novel regulators. We assume that barley can adapt flowering time to the environment via alternative routes within the pathway.

    更新日期:2020-01-24
  • Colourful cones: how did flower colour first evolve?
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-12-03
    Rudall P, Wellmer F.

    Angiosperms that are biotically pollinated typically produce flowers with bright and contrasting colours that help to attract pollinators and hence contribute to the reproductive success of the species. This colourful array contrasts with the much less multicoloured reproductive structures of the four living gymnosperm lineages, which are mostly wind pollinated, though cycads and Gnetales are predominantly pollinated by insects that feed on surface fluids from the pollination drops. This review examines the possible evolutionary pathways and cryptic clues for flower colour in both living and fossil seed plants. It investigates how the ancestral flowering plants could have overcome the inevitable trade-off that exists between attracting pollinators and minimizing herbivory, and explores the possible evolutionary and biological inferences from the colours that occur in some living gymnosperms. The red colours present in the seed-cone bracts of some living conifers result from accumulation of anthocyanin pigments; their likely primary function is to help protect the growing plant tissues under particular environmental conditions. Thus, the visual cue provided by colour in flower petals could have first evolved as a secondary effect, probably post-dating the evolution of bee colour vision but occurring before the subsequent functional accumulation of a range of different flower pigments.

    更新日期:2020-01-24
  • The role of epistasis and its interaction with environment in fine-tuning heading time in barley
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-23
    Christov N.

    This article comments on:Afsharyan NP, Sannemann W, Léon J, Ballvora A. 2020. Effect of epistasis and environment on flowering time of barley reveals novel flowering-delaying QTL allele. Journal of Experimental Botany 71, 893–906.

    更新日期:2020-01-24
  • Inter-plant communication via parasitic bridging
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-23
    Banerjee A.

    This article comments on:Li S, Zhang J, Liu H, Liu N, Shen G, Zhuang H, Wu J. 2020. Dodder-transmitted mobile signals prime host plants for enhanced salt tolerance. Journal of Experimental Botany 71, 1171–1184.

    更新日期:2020-01-24
  • Research on the genetic control of flowering in potato set to blossom
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-23
    Halford N.

    This article comments on:Seibert T, Abel C, Wahl V. 2020. Flowering time and the identification of floral marker genes in Solanum tuberosum ssp. andigena. Journal of Experimental Botany 71, 986–996.

    更新日期:2020-01-24
  • Role of chromatin modification and remodeling in stem cell regulation and meristem maintenance in Arabidopsis
    J. Exp. Bot. (IF 5.360) Pub Date : 2019-12-03
    Singh S, Singh A, Singh A, et al.

    In higher plants, pluripotent stem cells reside in the specialized microenvironment called stem cell niches (SCNs) harbored at the shoot apical meristem (SAM) and root apical meristem (RAM), which give rise to the aerial and underground parts of a plant, respectively. The model plant Arabidopsis thaliana (Arabidopsis) has been extensively studied to decipher the intricate regulatory mechanisms involving some key transcriptions factors and phytohormones that play pivotal roles in stem cell homeostasis, meristem maintenance, and organ formation. However, there is increasing evidence to show the epigenetic regulation of the chromatin architecture, gene expression exerting an influence on an innate balance between the self-renewal of stem cells, and differentiation of the progeny cells to a specific tissue type or organ. Post-translational histone modifications, ATP-dependent chromatin remodeling, and chromatin assembly/disassembly are some of the key features involved in the modulation of chromatin architecture. Here, we discuss the major epigenetic regulators and illustrate their roles in the regulation of stem cell activity, meristem maintenance, and related organ patterning in Arabidopsis.

    更新日期:2020-01-24
  • Leaf growth in early development is key to biomass heterosis in Arabidopsis
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-21
    Liu P, Peacock W, Wang L, et al.

    Arabidopsis thaliana hybrids have similar properties to hybrid crops with greater biomass relative to the parents. We asked whether the greater biomass was due to increased photosynthetic efficiency per unit leaf area or to overall increased leaf area and increased total photosynthate per plant. We found that photosynthetic parameters (electron transport rate, CO2 assimilation rate, chlorophyll content, chloroplast number) were unchanged on a leaf unit area and unit fresh weight basis between parents and hybrids indicating that heterosis is not a result of increased photosynthetic efficiency. To investigate the possibility of increased leaf area producing more photosynthate per plant we studied C24/ Landsberg erecta (Ler) hybrids in detail. These hybrids have earlier germination and leaf growth than the parents leading to a larger leaf area at any point in development of the plant. The developing leaves of the hybrids are significantly larger than those of the parents with consequent greater production of photosynthate and an increased contribution to heterosis. The set of leaves contributing to heterosis changes as the plant develops; the four most recently emerged leaves make the greatest contribution. As a leaf matures, its contribution to heterosis attenuates. While photosynthesis per unit leaf area is unchanged at any stage of development in the hybrid, leaf area is greater and the amount of photosynthate per plant is increased.

    更新日期:2020-01-23
  • Transposon-induced methylation of the RsMYB1 promoter disturbs the anthocyanin accumulation in red-fleshed radish (Raphanus sativus L.)
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-21
    Wang Q, Wang Y, Sun H, et al.

    Red-fleshed radish is a unique cultivar that is rich in anthocyanins beneficial to human health in taproot. However, the frequent occurrence of white-fleshed mutants affects the purity of commercially produced radish and mechanism has puzzled breeders for many years. In this study, we combined QTL-seq and transcriptome analyses to identify a candidate gene (RsMYB1) responsible for the anthocyanin accumulation in red-fleshed radish. However, no sequence variation was found in the coding and regulatory regions of the RsMYB1 genes of the red-fleshed (MTH01) and white-fleshed (JC01) lines, and a 7,372-bp CACTA transposon in the RsMYB1 promoter region occurred in both lines. A subsequent analysis suggested that the taproot white-fleshed mutant was the result of altered DNA methylation in the RsMYB1 promoter. This heritable epigenetic change was due to the hypermethylated CACTA transposon, which induced the spreading of DNA methylation to the promoter region of RsMYB1. Thus, RsMYB1 expression was considerably downregulated, which inhibited anthocyanin biosynthesis in white-fleshed mutants. An examination of transgenic radish calli and the results of a virus-induced gene silencing experiment confirmed the RsMYB1 is responsible for anthocyanins accumulation. Moreover, the mutant phenotype was partially eliminated by a treatment with a demethylating agent. This study explained the molecular regulation mechanism of appearance white-fleshed mutant in red-fleshed radish.

    更新日期:2020-01-23
  • Plant growth under suboptimal water conditions: early responses and methods to study them
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-22
    Dubois M, Inzé D.

    Drought stress forms a major environmental constraint during the life cycle of plants, often decreasing plant yield and in extreme cases threatening survival. The molecular and physiological responses induced by drought have therefore been the topic of extensive research during the last decades. Because soil-based approaches to study drought responses are often inconvenient due to low throughput and insufficient control of the conditions, osmotic stress assays in plates were developed to mimic drought. Addition of compounds such as poly-ethylene glycol, mannitol, sorbitol, or NaCl to controlled growth media has become increasingly popular since it offers the advantage of accurate control of stress level and onset. These osmotic stress assays enabled the discovery of very early stress responses, occurring within seconds or minutes following osmotic stress exposure. In this review, we construct a detailed timeline of early responses to osmotic stress, with a focus on how they initiate plant growth arrest. We further discuss the specific responses triggered by different types and severities of osmotic stress. Finally, we compare short-term plant responses under osmotic stress vs. in-soil drought and discuss the advantages, disadvantages and future of these plate-based proxies for drought.

    更新日期:2020-01-23
  • Exploiting natural variation in root system architecture via Genome Wide Association Studies
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-20
    Deja-Muylle A, Parizot B, Motte H, et al.

    Root growth and development has become an important research topic for breeders and researchers based on a growing need to adapt plants to changing and more demanding environmental conditions worldwide. Over the last few years, Genome Wide Association Studies (GWASs) became an important tool to identify the link between traits in the field and their genetic background. In this review, we give an overview of the current literature concerning GWASs performed on Root System Architecture (RSA) in plants. We summarize which root traits and approaches have been used for GWAS mentioning their respective success rate towards a successful gene discovery. Furthermore, we zoom in on the current technical hurdles in root phenotyping and GWAS and discuss future possibilities in this field of research.

    更新日期:2020-01-22
  • Calcium channel CNGC19 mediates basal defense signaling to balance colonization of Piriformospora indica on Arabidopsis roots
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-20
    Jogawat A, Meena M, Kundu A, et al.

    The activation of calcium signaling is a crucial event for perceiving environmental stress. Colonization by Piriformospora indica, a growth promoting root endosymbiont activates cytosolic Ca2+ in Arabidopsis roots. In this study, we analyze the role of calcium channels responsible for Ca2+ fluxes and its functional relevance. Expression profiling revealed that CNGC19 is a early activated gene, induced by unidentified components in P. indica cell wall extract. Functional analysis revealed that loss-of-function of CNGC19 results in growth inhibition by P.indica, due to increased colonization and loss of controlled P. indica growth. P. indicacell wall extract induced cytosolic Ca2+ elevation is reduced in cngc19 mutant indicating a role in generation of Ca2+cyt elevation. MAMP-trigerred immunity (MTI) is compromised in cngc19 lines as evident from unaltered callose deposition, reduced cis-OPDA, JA and JA-Ile levels and downregulation of jasmonate and other defense related genes which contributes to shift towards pathogenic response. Loss-of-function of CNGC19 results in inability to modulate indole glucosinolate content during P. indica-colonization. CNGC19 mediated basal immunity is AtPep receptor, PEPR dependent. CNGC19 is also crucial for P. indica mediated suppression of AtPep induced immunity. Thus, Arabidopsis CNGC19 is an important Ca2+ channel, maintaining a robust innate immunity and crucial for growth promotion signalling upon P. indica colonization.

    更新日期:2020-01-22
  • Mutations in orthologous PETALOSA TOE-type genes cause dominant double-flower phenotype in phylogenetically distant eudicots
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-21
    Gattolin S, Cirilli M, Chessa S, et al.

    The double-flower phenotype has been selected by humans for its attractiveness in various plant species and it is of great commercial value for the ornamental market. In this paper we investigated the genetic determinant of the dominant double-flower trait in carnation, petunia and Rosa rugosa, identifying mutant alleles of TARGET OF EAT (TOE)-type genes characterized by a disruption of the miR172 target sequence and of the C-terminal portion of the encoded protein. Despite the phylogenetic distance between these eudicots, which diverged in the early Cretaceous, the orthologous genes carrying such mutations all belong to a single TOE-type subgroup, herein referred to asPETALOSA(PET). Homology searches allowed us to identify PET sequences in various other species. To confirm the results on naturally occurring mutations, we used CrispR-Cas9 to induce lesions within the miR172 target site of Nicotiana tabacum PET genes, and this resulted in the development of supernumerary petaloid structures. This study describes pet alleles in economically important ornamentals and provides evidence about the possibility of identifying and engineering PET genes to obtain the desirable double-flower trait in different plants.

    更新日期:2020-01-22
  • Corrigendum to: Applications of chlorophyll fluorescence can improve crop production strategies: an examination of future possibilities
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-18
    Baker N, Rosenqvist E.

    Journal of Experimental Botany, (2004) 55(403): 1607–1627, doi: 10.1093/jxb/erh196

    更新日期:2020-01-21
  • Same same, but different: growth responses of primary and lateral roots
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-20
    Waidmann S, Sarkel E, Kleine-Vehn J.

    The root system architecture describes the shape and spatial arrangement of roots within the soil. Its spatial distribution depends on growth and branching rates as well as directional organ growth. The embryonic primary root gives rise to lateral (secondary) roots, and the ratio of both root types changes over the life span of a plant. Most studies have focused on the growth of primary roots and lateral root primordia development. Comparably less is known about the growth regulation of secondary root organs. Here, we review similarities and differences between primary and lateral root organ growth and particularly emphasize on how external stimuli and internal signals differentially integrate root system growth.

    更新日期:2020-01-21
  • A malectin domain kinesin functions in pollen and seed development in Arabidopsis
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-17
    Galindo-Trigo S, Grand T, Voigt C, et al.

    The kinesin family is greatly expanded in plants compared to animals and, with more than a third up-regulated in expression during cell division, it has been suggested that this expansion facilitated complex plant-specific cytoskeletal rearrangements. The cell cycle-regulated kinesins include two with an N-terminal malectin domain, a protein domain that has been shown to bind polysaccharides and peptides when found extracellularly in receptor-like kinases. Although malectin domain kinesins are evolutionarily deep-rooted, their function in plants remains unclear. Here we show that loss of MALECTIN DOMAIN KINESIN 2 (MDKIN2) results in stochastic developmental defects in pollen, embryo and endosperm. High rates of seed abnormalities and abortion occur in mdkin2 mutants through a partial maternal effect. No additive effect or additional developmental defects were noted in mdkin1 mdkin2 double mutants. MDKIN2 is expressed in regions of cell division throughout the plant. Subcellular localisation of MDKIN2 indicates a role in cell division, with a possible secondary function in the nuclei. Our results reveal a non-essential but important role for a malectin domain kinesin during development in plants.

    更新日期:2020-01-17
  • Aluminium/silicon interactions in higher plants- an update
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-17
    Hodson M, Evans D.

    Aluminium (Al) and silicon (Si) are abundant in soils, but their availability for plant uptake is limited by low solubility. However, Al toxicity is a major problem in naturally occurring acid soils and in soils affected by acidic precipitation. When, in 1995, we reviewed this topic for the Journal of Experimental Botany, it was clear that under certain circumstances soluble Si could ameliorate the toxic effects of Al, an effect mirrored in organisms beyond the plant kingdom. In the 25 years since our review, it has become evident that the amelioration phenomenon occurs in the root apoplast, with the formation of hydroxyaluminosilicates being part of the mechanism. A much better knowledge of the molecular basis for Si and Al uptake by plants and of Al toxicity mechanisms has been developed. However, relating this work to amelioration by Si is at an early stage. It is now clear that co-deposition of Al and Si in phytoliths is a fairly common phenomenon in the plant kingdom, and this may be important in detoxification of Al. Relatively little work on Al/Si interactions in field situations has happened in the last 25 years, and this is a key area for future development.

    更新日期:2020-01-17
  • The non-photochemical quenching protein LHCSR3 prevents oxygen-dependent photoinhibition in Chlamydomonas reinhardtii
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-16
    Roach T, Na C, Stöggl W, et al.

    Non-photochemical quenching (NPQ) helps dissipate surplus light energy, preventing formation of reactive oxygen species (ROS). In Chlamydomonas reinhardtii the thylakoid membrane protein LHCSR3 is involved in pH-dependent (qE-type) NPQ, deficient in the npq4 mutant. Preventing PSII repair revealed that npq4 lost PSII activity faster than wild-type (WT) in elevated O2, while no difference between strains was observed in O2-deplete conditions. Low Fv/Fm values remained 1.5 h after moving cells out of high light, and this qH-type quenching was independent of LHCSR3 and not accompanied by losses of maximum PSII activity. Culturing cells in historic O2 atmospheres (30-35%) increased the qE of cells, due to increased LHCSR1 and PsbS levels, and LHCSR3 in WT, showing that atmospheric O2 tensions regulate qE capacity. Colony growth of npq4 was severely restricted at elevated O2 and npq4 accumulated more reactive electrophile species (RES) than WT, which could damage PSI. Levels of PsaA (PSI) were lower in npq4 grown at 35 % O2 while PsbA (PSII) levels remained stable. We conclude that even at high O2 concentrations, the PSII repair cycle is sufficient to maintain net levels of PSII. However, LHCSR3 has an important function in protecting PSI against O2-mediated damage, e.g. via RES.

    更新日期:2020-01-16
  • An allelic variant in GAME9 determines its binding capacity to the GAME17 promoter in the regulation of steroidal glycoalkaloid biosynthesis in tomato
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-14
    Yu G, Li C, Zhang L, et al.

    Steroidal glycoalkaloids (SGAs) are cholesterol-derived molecules found in the Solanaceae family. SGA content varies among different plant species and varieties. However, the genetic mechanisms regulating SGA content remain unclear. Here, we demonstrate that genetic variation in GLYCOALKALOID METABOLISM 9 (GAME9) is responsible for the variation in SGA content in tomato (Solanum lycopersicum). During a sequential analysis we found a one base pair substitution in the AP2/ERF binding domain of GAME9. The one base pair substitution in GAME9 was significantly associated with high SGA content and determined its binding capacity with the promoter of GAME17, a core SGA biosynthesis gene. The High-SGA GAME9 allele is mainly present in the S. pimpinellifolium (PIM) and S. lycopersicum var. cerasiforme (CER) populations and encodes a protein that can bind the GAME17 promoter. In contrast, the Low-SGA GAME9 allele is mainly present in the big-fruited varieties of S. lycopersicum (BIG) population and encodes a protein that show weakly bind the GAME17 promoter. Our findings provide new insight into the regulation of SGA biosynthesis and the factors that affect the accumulation of SGA in tomato.

    更新日期:2020-01-15
  • Live-cell imaging of early events following pollen perception in self-incompatible Arabidopsis sthaliana
    J. Exp. Bot. (IF 5.360) Pub Date : 2020-01-14
    Rozier F, Riglet L, Kodera C, et al.

    Early events occurring at the surface of the female organ are critical for plant reproduction, especially in species with a dry stigma. Following landing on the stigmatic papilla cells, the pollen hydrates and germinates a tube, which penetrates the cell wall and grows towards the ovules to convey the male gametes to the embryo sac. In self-incompatible (SI) species within the Brassicaceae, these processes are blocked when the stigma encounters an incompatible pollen. Here, based on the generation of SI-Arabidopsis lines and by setting up a live imaging system, we showed that control of pollen hydration has a central role in pollen selectivity. The faster pollen pumps water from the papilla during an initial period of 10 minutes, the faster it germinates. Furthermore, we found that the SI barriers act to block the proper hydration of incompatible pollen and when hydration is promoted by high humidity, an additional control prevents pollen tube penetration into the stigmatic wall. In papilla cells, actin bundles focalize at the contact site with the compatible pollen but not with the incompatible one, raising the possibility that stigmatic cells react to the mechanical pressure applied by the invading growing tube.

    更新日期:2020-01-15
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