植物科学顶尖文章导读|11月1-5日

植物学顶尖杂志 Plant Cell, New Phytol , Mol Plant, Plant Physiol, Plant Biotechnol  J, Plant J, nature Plants及综合期刊Nucleic Acids Res. ， PNAS，NB，NC及NG有关植物学的研究文章导读，每日定时更新，了解行业最前沿进展。

Stomatal movements depend on the transport and metabolism of osmotic solutes that drive reversible changes in guard cell volume and turgor. These processes are defined by a deep knowledge of the identities of the key transporters and of their biophysical and regulatory properties, and have been modelled successfully with quantitative kinetic detail at the cellular level. Transpiration of the leaf and canopy, by contrast, is described by quasi-linear, empirical relations for the inputs of atmospheric humidity, CO2, and light, but without connection to guard cell mechanics. Until now, no framework has been available to bridge this gap and provide an understanding of their connections. Here we introduce OnGuard2, a quantitative systems platform that utilizes the molecular mechanics of ion transport, metabolism and signalling of the guard cell to define the water relations and transpiration of the leaf. We show that OnGuard2 faithfully reproduces the kinetics of stomatal conductance in Arabidopsis, its dependence on vapor pressure difference (VPD) and on water feed to the leaf. OnGuard2 also predicted with VPD unexpected alterations in K+ channel activities, and changes in stomatal conductance of the slac1 Cl- channel and ost2 H+-ATPase mutants which we verified experimentally. OnGuard2 thus bridges the micro-macro divide, offering a powerful tool with which to explore the links between guard cell homeostasis, stomatal dynamics and foliar transpiration.

http://www.plantcell.org/content/early/2017/11/01/tpc.17.00694

Phosphorylation of the RNA polymerase II (Pol II) C-terminal domain (CTD) regulates transcription of protein-coding mRNAs and non-coding RNAs (ncRNAs). CTD function in transcription of protein-coding RNAs has been studied extensively, but its role in plant ncRNA transcription remains obscure. Here, using Arabidopsis thaliana CTD PHOSPHATASE-LIKE 4 knock-down lines (CPL4RNAi), we showed that CPL4 functions in genome-wide, conditional production of 3'-extensions of small nuclear RNAs (snRNAs) and biogenesis of novel transcripts from protein-coding genes downstream of the snRNAs (snRNA-Downstream Protein-coding Genes, snR-DPGs). Production of snR-DPGs required the Pol II snRNA promoter (PIIsnR), and CPL4RNAi plants showed increased read-through of the snRNA 3'-end processing signal, leading to continuation of transcription downstream of the snRNA gene. We also discovered an unstable, intermediate-length RNA from the SMALL SCP1-LIKE PHOSPHATASE 14 locus (imRNASSP14), whose expression originated from the 5' region of a protein-coding gene. Expression of the imRNASSP14 was driven by a PIIsnR and was conditionally 3'-extended to produce an mRNA. In wild type, salt stress induced the snRNA-to-snR-DPG switch, which was associated with alterations of Pol II-CTD phosphorylation at the target loci. The snR-DPG transcripts occur widely in plants, suggesting that the transcriptional snRNA-to-snR-DPG switch may be a ubiquitous mechanism to regulate plant gene expression in response to environmental stresses.

http://www.plantcell.org/content/early/2017/11/01/tpc.17.00331

To explore the genetic robustness (canalization) of metabolism, we examined the levels of fruit metabolites in multiple harvests of a tomato introgression line (IL) population. The IL partitions the whole genome of the wild species Solanum pennellii in the background of the cultivated tomato (Solanum lycopersicum). We identified several metabolite quantitative trait loci that reduce variability for both primary and secondary metabolites, which we named canalization metabolite quantitative trait loci (cmQTLQTL). We validates nine cmQTLQTL using an independent population of backcross inbred lines, derived from the same parents, which allows increased resolution in mapping the QTL previously identified in the ILs. These cmQTLQTL showed little overlap with QTLQTL for the metabolite levels themselves. Moreover, the intervals they mapped to harbored few metabolism-associated genes, suggesting that the canalization of metabolism is largely controlled by regulatory genes.

http://www.plantcell.org/content/early/2017/11/01/tpc.17.00367

Aluminium-activated malate transporters (ALMT) form a family of anions channels in plants but little is known about most of its members. This study examined the function of OsALMT4 from rice (Oryza sativa L.). We show that OsALMT4 is expressed in roots and shoots and the OsALMT4 protein localizes to the plasma membrane. Transgenic rice lines over-expressing (OX) OsALMT4 released malate from the roots constitutively and had two-fold higher malate concentrations in the xylem sap than nulls indicating greater concentrations of malate in the apoplast. OX lines developed brown necrotic spots on the leaves which did not appear on nulls. These symptoms were not associated with altered concentrations of any mineral element in the leaves although the OX lines had higher concentrations of Mn and B in their grain compared with nulls. While total leaf Mn concentrations were not different between the OX and null lines, Mn concentrations in the apoplast were greater in the OX plants. The OX lines also displayed increased expression of Mn transporters and were more sensitive to Mn toxicity than null plants. We showed that growth of wild-type rice was unaffected by 100 µM Mn in hydroponics but, when combined with 1 mM malate, this concentration inhibited growth. We conclude that increasing OsALMT4 expression affected malate efflux and compartmentation within the tissues which increased Mn concentrations in the apoplast of leaves and induced the toxicity symptoms. This study reveals new links between malate transport and mineral nutrition.

http://www.plantphysiol.org/content/early/2017/11/03/pp.17.01142

Increasing grain yield is an endless challenge for cereal crop breeding. In barley, grain number is mainly controlled by Six-rowed spike 1 (Vrs1) that encodes a homeodomain leucine zipper class I transcription factor. However, little is known about the genetic basis of grain size. Here we show that extreme suppression of lateral florets contributes to enlarged grains in deficiens barley. Through a combination of fine mapping and resequencing deficiens mutants we have identified that a single amino acid substitution at a putative phosphorylation site in VRS1 is responsible for the deficiens phenotype. deficiens mutant alleles confer an increase in grain size, reduction in plant height and a significant increase in thousand grain weight in contemporary cultivated germplasm. Haplotype analysis revealed that barley carrying the deficiens allele (Vrs1.t1) originated from two-rowed types carrying the Vrs1.b2 allele, predominantly found in germplasm from Northern Africa. In situ hybridization of histone H4, a marker for cell cycle or proliferation, showed weaker expression in the lateral spikelets compared to central spikelets in deficiens. Transcriptome analysis revealed that a number of histone superfamily genes were upregulated in the deficiens mutant suggesting that enhanced cell proliferation in the central spikelet may contribute to larger grains. Our data suggest that grain yield can be improved by suppressing the development of specific organs that are not positively involved in sink/source relationships.

Nonhost resistance is defined as the immunity of a plant species to all nonadapted pathogen species. Arabidopsis ecotype Columbia-0 (Col-0) is nonhost to oomycete plant pathogen Phytophthora sojae and fungal plant pathogen Fusarium virguliforme that are pathogenic to soybean. Previously, we reported generating pss1 mutation in the pen1-1 genetic background, genetic mapping and characterization of the Arabidopsis nonhost resistance Phytophthora sojae susceptible gene locus, PSS1. In this study, we identified six candidate PSS1 genes by comparing single nucleotide polymorphisms (SNPs) of (i) the bulked DNA sample of seven F2:3 families homozygous for the pss1 allele and (ii) the pen1-1 mutant with Col-0. Analyses of T-DNA insertion mutants for each of these candidate PSS1 genes identified the At3g59640 gene encoding a glycine rich protein as the putative PSS1 gene. Later, complementation analysis confirmed the identity of At3g59640 as the PSS1 gene. PSS1 is induced following P. sojae infection as well as expressed in an organ-specific manner. Co-expression analysis of the available transcriptomic data followed by reverse transcriptase PCR suggested that PSS1 is co-regulated with ATG8a (At4g21980), a core gene in autophagy. PSS1 contains a predicted single membrane spanning domain. Subcellular localization study indicated that it is an integral plasma membrane protein. Sequence analysis suggested that soybean unlikely contains a PSS1-like defense function. Following introduction of PSS1 into the soybean cultivar 'Williams 82', the transgenic plants exhibited enhanced resistance to F. virguliforme, the pathogen that causes sudden death syndrome.

In maize, Bundle sheath defective 2 (BSD2) plays an essential role in Rubisco biogenesis, and is required for correct bundle sheath (BS) cell differentiation. Yet, BSD2 RNA and protein levels are similar in mesophyll (M) and BS chloroplasts, although Rubisco accumulates only in BS chloroplasts. This raises the possibility of additional BSD2 roles in cell development. To test this hypothesis, transgenic lines were created that over- and under-express BSD2 in both BS and M cells, driven by the cell type-specific RBCS or PEPC promoters, or the ubiquitin promoter. Genetic crosses showed that each of the transgenes could complement Rubisco deficiency and seedling lethality conferred by the bsd2 mutation. This was unexpected, as RBCS-BSD2 lines lacked BSD2 in mesophyll chloroplasts, and PEPC-BSD2 lines expressed half the wild-type BSD2 level in BS chloroplasts. We conclude that BSD2 does not play a vital role in M cells, and that BS BSD2 is in excess of requirements for Rubisco accumulation. BSD2 levels did affect chloroplast coverage in BS cells. In PEPC-BSD2 lines, chloroplast coverage decreased 30-50%, whereas lines with increased BSD2 content exhibited a 25% increase. This suggests that BSD2 has an ancillary role in BS cells related to chloroplast size. Gas exchange showed decreased photosynthetic rates in PEPC-BSD2 lines despite restored Rubisco function, correlating with reduced chloroplast coverage and pointing to CO2 diffusion changes. Conversely, increased chloroplast coverage did not result in increased Rubisco abundance or photosynthetic rates. This suggests another limitation beyond chloroplast volume, most likely Rubisco biogenesis and/or turnover rates.

Soil acidity and waterlogging increase manganese (Mn) in leaf tissues to potentially toxic concentrations, an effect reportedly alleviated by increased silicon (Si) and phosphorus (P) supply. Effects of Si and P on Mn toxicity were studied in four plant species using synchrotron-based micro X-ray fluorescence (μ-XRF) and nanoscale secondary ion mass spectrometry (NanoSIMS) to determine Mn distribution in leaf tissues and using synchrotron-based X-ray absorption spectroscopy (XAS) to measure Mn speciation in leaves, stems and roots. A concentration of 30 μM Mn in solution was toxic to cowpea and soybean, with 400 μM Mn toxic to sunflower but not white lupin. Unexpectedly, μ-XRF analysis revealed that 1.4 mM Si in solution decreased Mn toxicity symptoms through increased Mn localization in leaf tissues. NanoSIMS showed Mn and Si co-localized in the apoplast of soybean epidermal cells and basal cells of sunflower trichomes. Concomitantly, added Si decreased oxidation of Mn(II) to Mn(III) and Mn(IV). An increase from 5 to 50 μM P in solution changed some Mn toxicity symptoms but had little effect on Mn distribution or speciation. We conclude that Si increases localized apoplastic sorption of Mn in cowpea, soybean and sunflower leaves thereby decreasing free Mn2+ accumulation in the apoplast or cytoplasm.

Angiosperm adaptations to seasonally cold climates have occurred multiple times independently. However, the observation that less than half of all angiosperm families are represented in temperate latitudes suggests internal constraints on the evolution of cold tolerance/avoidance strategies. Similar to angiosperms as a whole, grasses are primarily tropical, but one major clade, subfamily Pooideae, radiated extensively within temperate regions. It is posited that this Pooideae niche transition was facilitated by an early origin of long-term cold responsiveness around the base of the subfamily, and that a set of more ancient pathways enabled evolution of seasonal cold tolerance.To test this, we compared transcriptome-level responses of disparate Pooideae to short-/long-term cold and with those previously known in the subtropical grass rice (Ehrhartoideae).Analyses identified several highly conserved cold-responsive ‘orthogroups’ within our focal Pooideae species that originated successively during the diversification of land plants, predominantly via gene duplication. The majority of conserved Pooideae cold-responsive genes appear to have ancient roles in stress responses, with most of the orthogroups also being sensitive to cold in rice. However, a subgroup of genes was likely co-opted de novo early in the Pooideae.These results highlight a plausible stepwise evolutionary trajectory for cold adaptations across Pooideae.

There is increasing knowledge on the diversity of root-endophytic fungi, but limited information on their lifestyles and dependence on hosts hampers our understanding of their ecological functions. We compared diversity and biogeographical patterns of cultivable and noncultivable root endophytes to assess whether their occurrence is determined by distinct ecological factors.The endophytic diversity in roots of nonmycorrhizal Microthlaspi spp. growing across Europe was assessed using high-throughput sequencing (HTS) and compared with a previous dataset based on cultivation of endophytes from the same root samples.HTS revealed a large fungal richness undetected by cultivation, but which largely comprised taxa with restricted distributions and/or low representation of sequence reads. Both datasets coincided in a consistent high representation of widespread endophytes within orders Pleosporales, Hypocreales and Helotiales, as well as similar associations of community structure with spatial and environmental conditions. Likewise, distributions of particular endophytes inferred by HTS agreed with cultivation data in suggesting individual ecological preferences.Our findings support that Microthlaspi spp. roots are colonized mostly by saprotrophic and likely facultative endophytes, and that differential niche preferences and distribution ranges among fungi importantly drive the assembly of root-endophytic communities.

http://onlinelibrary.wiley.com/doi/10.1111/nph.14873/full

Photosynthetic organisms such as plants, algae and some cyanobacteria synthesize tocochromanols, a group of compounds that encompasses tocopherols and tocotrienols and that exhibits vitamin E activity in animals. While most vitamin E biosynthetic genes have been identified in plant genomes, regulatory genes controlling tocopherol accumulation are currently unknown.We isolated by forward genetics Arabidopsis enhanced vitamin E (eve) mutants that overaccumulate the classic tocopherols and plastochromanol-8, and a tocochromanol unknown in this species. We mapped eve1 and eve4, and identified the unknown Arabidopsis tocochromanol by using a combination of analytical tools. In addition, we determined its biosynthetic pathway with a series of tocochromanol biosynthetic mutants and transgenic lines.eve1 and eve4 are two seed lipid mutants affecting the WRINKLED1 (WRI1) and ACYL-COA:DIACYLGLYCEROL ACYLTRANSFERASE1 (DGAT1) genes, respectively. The unknown tocochromanol is 11′-12′ γ-tocomonoenol, whose biosynthesis is VITAMIN E 1 (VTE1) - and VTE2-dependent and is initiated by the condensation of homogentisate (HGA) and tetrahydrogeranylgeranyl pyrophosphate.

This study identifies the first two regulatory genes, WRI1 and DGAT1, that control the synthesis of all tocochromanol forms in seeds, and shows the existence of a metabolic trade-off between lipid and tocochromanol metabolisms. Moreover, it shows that Arabidopsis possesses a tocomonoenol biosynthetic pathway that competes with tocopherol synthesis.

http://onlinelibrary.wiley.com/doi/10.1111/nph.14856/full

Root knot nematodes (RKNs) penetrate into the root vascular cylinder, triggering morphogenetic changes to induce galls, de novo formed ‘pseudo-organs’ containing several giant cells (GCs). Distinctive gene repression events observed in early gall/GCs development are thought to be mediated by post-transcriptional silencing via microRNAs (miRNAs), a process that is far from being fully characterized. Arabidopsis thaliana backgrounds with altered activities based on target 35S::MIMICRY172(MIM172), 35S::TARGET OF EARLY ACTIVATION TAGGED 1 (TOE1)-miR172-resistant (35S::TOE1R) and mutant (flowering locus T-10 (ft-10)) lines were used for functional analysis of nematode infective and reproductive parameters. The GUS-reporter lines, MIR172A–E::GUS, treated with auxin (IAA) and an auxin-inhibitor (a-(phenyl ethyl-2-one)-indole-3-acetic acid (PEO-IAA)), together with the MIR172C AuxRE::GUS line with two mutated auxin responsive elements (AuxREs), were assayed for nematode-dependent gene expression. Arabidopsis thaliana backgrounds with altered expression of miRNA172, TOE1 or FT showed lower susceptibility to the RKNs and smaller galls and GCs. MIR172C−D::GUS showed restricted promoter activity in galls/GCs that was regulated by auxins through auxin-responsive factors. IAA induced their activity in galls while PEO-IAA treatment and mutations in AuxRe motifs abolished it.The results showed that the regulatory module miRNA172/TOE1/FT plays an important role in correct GCs and gall development, where miRNA172 is modulated by auxins.

http://onlinelibrary.wiley.com/doi/10.1111/nph.14839/full

Systemin (SYS), an octadecapeptide hormone processed from a 200-amino-acid precursor (prosystemin, PS), plays a central role in the systemic activation of defense genes in tomato in response to herbivore and pathogen attacks. However, whether PS mRNA is transferable and its role in systemic defense responses remain unknown. We created the transgenic tomato PS gene tagged with the green fluorescent protein (PS-GFP) using a shoot- or root-specific promoter, and the constitutive 35S promoter in Arabidopsis. Subcellular localization of PS-/SYS-GFP was observed using confocal laser scanning microscopy and gene transcripts were determined using quantitative real-time PCR. In Arabidopsis, PS protein can be processed and SYS is secreted. Shoot-/root-specific expression of PS-GFP in Arabidopsis, and grafting experiments, revealed that the PS mRNA moves in a bi-directional manner. We also found that ectopic expression of PS improves Arabidopsis resistance to the necrotrophic fungus Botrytis cinerea, consistent with substantial upregulation of the transcript levels of specific pathogen-responsive genes. Our results provide novel insights into the multifaceted mechanism of SYS signaling transport and its potential application in genetic engineering for increasing pathogen resistance across diverse plant families.

http://onlinelibrary.wiley.com/doi/10.1111/nph.14858/full