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植物学顶尖杂志 Plant Cell, New Phytologist, Molecular Plant, Plant Physiol, Plant Biotechnology Journal, Plant Journal及nature Plant 杂志每日最新文章导读，了解行业最前沿进展。

Nature Plants

Rice (Oryza sativa L.) is a staple food for more than half of the world's population. To meet the ever-increasing demand for food, because of population growth and improved living standards, world rice production needs to double by 20301. The development of new elite rice varieties with high yield and superior quality is challenging for traditional breeding approaches, and new strategies need to be developed. Here, we report the successful development of new elite varieties by pyramiding major genes that significantly contribute to grain quality and yield from three parents over five years. The new varieties exhibit higher yield potential and better grain quality than their parental varieties and the China's leading super-hybrid rice, Liang-you-pai-jiu (LYP9 or Pei-ai 64S/93-11). Our results demonstrate that rational design is a powerful strategy for meeting the challenges of future crop breeding, particularly in pyramiding multiple complex traits.

http://www.nature.com/articles/nplants201731

Plants uptake nitrogen (N) from the soil mainly in the form of nitrate. However, nitrate is often distributed heterogeneously in natural soil. Plants, therefore, have a systemic long-distance signalling mechanism by which N starvation on one side of the root leads to a compensatory N uptake on the other N-rich side1,2. This systemic N acquisition response is triggered by a root-to-shoot mobile peptide hormone, C-TERMINALLY ENCODED PEPTIDE (CEP), originating from the N-starved roots3,4, but the molecular nature of the descending shoot-to-root signal remains elusive. Here, we show that phloem-specific polypeptides that are induced in leaves upon perception of root-derived CEP act as descending long-distance mobile signals translocated to each root. These shoot-derived polypeptides, which we named CEP DOWNSTREAM 1 (CEPD1) and CEPD2, upregulate the expression of the nitrate transporter gene NRT2.1 in roots specifically when nitrate is present in the rhizosphere. Arabidopsis plants deficient in this pathway show impaired systemic N acquisition response accompanied with N-deficiency symptoms. These fundamental mechanistic insights should provide a conceptual framework for understanding systemic nutrient acquisition responses in plants.

http://www.nature.com/articles/nplants201729

It remains unclear how post-transcriptional gene silencing (PTGS) in plants discriminates aberrant RNAs from canonical messenger RNAs (mRNAs). The key step of plant PTGS is the conversion of aberrant RNAs into double-stranded RNAs by RNA-DEPENDENT RNA POLYMERASE6 (RDR6). Here, we show that RDR6 itself selects aberrant poly(A)-less mRNAs over canonical polyadenylated mRNAs as templates at the initiation step of complementary strand synthesis. This mechanism can be viewed as an innate safeguard against ‘self-attack’ by PTGS.

http://www.nature.com/articles/nplants201736

Vascular plants rely on differences in osmotic pressure to export sugars from regions of synthesis (mature leaves) to sugar sinks (roots, fruits). In this process, known as Münch pressure flow, the loading of sugars from photosynthetic cells to the export conduit (the phloem) is crucial, as it sets the pressure head necessary to power long-distance transport. Whereas most herbaceous plants use active mechanisms to increase phloem sugar concentration above that of the photosynthetic cells, in most tree species, for which transport distances are largest, loading seems, counterintuitively, to occur by means of passive symplastic diffusion from the mesophyll to the phloem. Here, we use a synthetic microfluidic model of a passive loader to explore the non-linear dynamics that arise during export and determine the ability of passive loading to drive long-distance transport. We first demonstrate that in our device, the phloem concentration is set by the balance between the resistances to diffusive loading from the source and convective export through the phloem. Convection-limited export corresponds to classical models of Münch transport, where the phloem concentration is close to that of the source; in contrast, diffusion-limited export leads to small phloem concentrations and weak scaling of flow rates with hydraulic resistance. We then show that the effective regime of convection-limited export is predominant in plants with large transport resistances and low xylem pressures. Moreover, hydrostatic pressures developed in our synthetic passive loader can reach botanically relevant values as high as 10 bars. We conclude that passive loading is sufficient to drive long-distance transport in large plants, and that trees are well suited to take full advantage of passive phloem loading strategies.

http://www.nature.com/articles/nplants201732

New Phytologist

Understanding the origin and evolution of complex traits is a majorgoal in biology. Here, we addressed how cellular novelties translate to trait innovation in the context of explosive seed dispersal. We followed a comparative approach by studying seed dispersal in the Arabidopsis thaliana relative, Cardamine hirsuta. This plant is a widespread, ruderal species that uses explosive seed dispersal to successfully colonize disturbed habitats. We recently presented a mathematical model that explains the mechanism of explosi ve dispersal in C. hirsuta (Hofhuis et al., 2016). Here, we review the cellular innovations for the storage and rapid release of energy that underpin the evolution of this trait. The mechanism that we proposed for establishing pre-tension in the fruit depends on a particular cell shape in the exocarp layer. We analyze the phylogenetic distribution of exocarp cell shape in Cardamine species with explosive fruit, and other species in the Brassicaceae with nonexplosive fruit. We conclude that this was an enabling character for the origin of explosive seed dispersal, while a second character gain – asymm etric lignification of the endocarp b cell layer – was a driving character.

http://onlinelibrary.wiley.com/doi/10.1111/nph.14541/abstract

Manganese (Mn) is an essential constituent of photosystem II (PSII) and therefore indispensable for oxygenic photosynthesis. Very little is known about how Mn is transported, delivered and retained in photosynthetic cells. Recently, the thylakoid-localized transporter PAM71 has been linked to chloroplast Mn homeostasis in Arabidopsis thaliana. Here, we characterize the function of its homolog in Synechocystis (SynPAM71) . We used a loss-of-function line (ΔSynPAM71), wild-type (WT) cells exposed to Mn stress and strains expressing a tagged variant ofSynPAM71 to characterize the role of SynPAM71 in cyanobacterial Mn homeostasis.The ΔSynPAM71 strain displays an Mn-sensitive phenotype with reduced levels of chlorophyll and PSI accumulation, defects in PSII photochemistry and intracellular Mn enrichment, particularly in the thylakoid membranes. These effects are attributable to Mn toxicity, as very similar symptoms were observed in WT cells exposed to excess Mn. Moreover, CyanoP, which is involved in the early steps of PSII assembly, is massively upregulated in ΔSynPAM71. SynPAM71 was detected in both the plasma membrane and, to a lesser extent, the thylakoid membranes. Our results suggest that SynPAM71 is involved in the maintenance of Mn homeostasis through the export of Mn from the cytoplasm into the periplasmic and luminal compartments, where it can be stored without interfering with cytoplasmic metabolic processes.

http://onlinelibrary.wiley.com/doi/10.1111/nph.14526/abstract

Mitochondrial respiration often appears to be inhibited in the light when compared with measurements in the dark. This inhibition is inferred from the response of the net CO2assimilation rate (A) to absorbed irradiance (I), changing slope around the light compensation point (Ic). We suggest a model that provides a plausible mechanistic explanation of this ‘Kok effect’.The model uses the mathematical description of photosynthesis developed by Farquhar, von Caemmerer and Berry; it involves no inhibition of respiration rate in the light. We also describe a fitting technique for quantifying the Kok effect at low I. Changes in the chloroplastic CO2 partial pressure (Cc) can explain curvature of A vs I, its diminution in C4 plants and at low oxygen concentrations or high carbon dioxide concentrations in C3 plants, and effects of dark respiration rate and of temperature. It also explains the apparent inhibition of respiration in the light as inferred by the Laisk approach. While there are probably other sources of curvature in A vs I, variation in Cc can largely explain the curvature at low irradiance, and suggests that interpretation of day respiration compared with dark respiration of leaves on the basis of the Kok effect needs reassessment.

http://onlinelibrary.wiley.com/doi/10.1111/nph.14512/abstract

The 18th New Phytologis t Workshop was dedicated to possible causes of the Kok effect, the ty pical break in the light response curve of net photosynthesis. Available data obtained since its discovery in 1948 show that the effect is not purely caused by a down-regulation of respiration, contrary to the commonly accepted view. However, estimates of leaf respiratory rates obtained in various ecosystems with techniques including the Kok method appear to be widely consistent across different studies, suggesting that Kok-derived values can be used as a surrogate for actual day respiration values.

http://onlinelibrary.wiley.com/doi/10.1111/nph.14526/abstract

Plant Physiology

The light harvesting chlorophyll (Chl) a/b complex of photosystem II (LHCII) is able to switch to multiple functions under different light conditions, i.e. harvesting solar energy for photosynthesis and dissipating excess excitation energy for photoprotection. The role of the different carotenoids (Cars) bound to LHCII in regulating the structure and function of the complex is a long-lasting question in photosynthesis research. 9-cis-neoxanthin (Nx) is one of the important Cars, which can only be found in the light harvesting Chla/b complexes of photosystem II. High-resolution structural analysis of LHCII shows that Nx is located between different monomeric LHCIIs, with one side protruding into the lipid membrane. In this paper, the various functional significances of this unique feature of the Nx binding in LHCII are studied with the in vitro reconstituted LHCIIs both with and without Nx, and the native complexes isolated either from wild type Arabidopsis, or from its mutant aba4-3 lacking Nx. Our results reveal that binding of Nx affects the binding affinity of violaxanthin (Vx) to LHCII significantly. In the absence of Nx, Vx has a much higher binding affinity to trimeric LHCII. The strong coordination between Nx and Vx at the interfaces of adjacent monomers of LHCII plays an important role both in operating the xanthophyll cycle and in transient modulation of the non-photochemical quenching.

http://www.plantphysiol.org/content/early/2017/03/20/pp.17.00029.abstract

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