从细菌、酵母及植物多糖合成酶的调控看花粉管胼胝质酶的调控(英文)

多糖作为结构和能量贮存分子是植物重要的组成成分。植物细胞壁主要成分为多糖。细胞壁在确定细胞生长、形状方面起重要作用,细胞壁还参与细胞的营养吸收、信息传递,也是防止外源对细胞不良影响的第一道防线。不同植物细胞壁的多糖成分可作为食品、建筑及造纸的原料,具有广泛的工业价值。通过描述细菌、酵母及植物多糖合成酶的机制,推断花粉管胼胝质合成酶的可能调控机制。

Drought Responses of Leaf Tissues from Wheat Cultivars of Differing Drought Tolerance at the Metabolite Level

Drought has serious effects on the physiology of cereal crops. At the cellular and specifically the metabolite level, many individual compounds are increased to provide osmoprotective functions, prevent the dissociation of enzymes, and to decrease the number of reactive oxygen species present in the cell. We have used a targeted GC-MS approach to identify compounds that differ in three different cultivars of bread wheat characterized by different levels of tolerance to drought under drought stress （Kukri, intolerant; Excalibur and RAC875, tolerant）. Levels of amino acids, most notably proline, tryptophan, and the branched chain amino acids leucine, isoleucine, and valine were increased under drought stress in all cultivars. In the two tolerant cultivars, a small decrease in a large number of organic acids was also evident. Excalibur, a cultivar genotypically related to Kukri, showed a pattern of response that was more similar to Kukri under well-watered conditions. Under drought stress, Excalibur and RAC875 had a similar response; however, Excalibur did not have the same magnitude of response as RAC875. Here, the results are discussed in the context of previous work in physiological and proteomic analyses of these cultivars under drought stress.

Characterization of Ion Contents and Metabolic Responses to Salt Stress of Different Arabidopsis AtHKT1;1 Genotypes and Their Parental Strains

Plants employ several strategies to maintain cellular ion homeostasis under salinity stress, including mediat-ing ion fluxes by transmembrane transport proteins and adjusting osmotic pressure by accumulating osmolytes. The HKT （high-affinity potassium transporter） gene family comprises Na^＋ and Na^＋/K^＋ transporters in diverse plant species, with HKT1,1 as the only member in Arabidopsis thaliana. Cell-type-specific overexpression of AtHKT1;1 has been shown to prevent shoot Na^＋ overaccumulation under salinity stress. Here, we analyzed a broad range of metabolites and elements in shoots and roots of different AtHKT1;1 genotypes and their parental strains before and after salinity stress, revealing a reciprocal relationship of metabolite differences between an AtHKT1;1 knockout line （hktl;1） and the AtHKT1;1 overex- pressing lines （E2586 UASGAL4：HKT1;1 and J2731＊UASGAL4：HKT1;1）. Although levels of root sugars were increased after salt stress in both AtHKTI,1 overexpressing lines, E2586 UASGAL4：HKT1;1 showed higher accumulation of the osmopro-tectants trehalose, gentiobiose, and melibiose, whereas J2731＊UASGAL4：HKT1;1 showed higher levels of sucrose and raffinose, compared with their parental lines, respectively. In contrast, the knockout line hktl,1 showed strong increases in the levels of the tricarboxylic acid （TCA） cycle intermediates in the shoots after salt treatment. This coincided with a significant depletion of sugars, suggesting that there is an increased rate of carbon influx into the TCA cycle at a constant rate of C-efflux from the cycle, which might be needed to support plant survival during salt stress. Using correlation analysis, we identified associations between the Na^＋ content and several sugars, suggesting that regulation of sugar metabolism is important in plant responses to salinity stress.

KNAT7 positively regulates xylan biosynthesis by directly activating IRX9 expression in Arabidopsis

Xylan is the major plant hemicellulosic poly- saccharide in the secondary cell wall. The transcription factor KNOTTED-LIKE HOMEOBOX OF ARABIDOPSIS THALIANA 7 （KNAT7） regulates secondary cell wall biosynthesis, but its exact role in regulating xylan biosynthesis remains unclear. Using transactivation analyses, we demonstrate that KNAT7 activates the promoters of the xylan biosynthetic genes, IRREGULAR XYLEM 9 （IRX9）, IRX10, IRREGULAR XYLEM 14-LIKE （IRX14L）, and FRAGILE FIBER 8 （FRAS）. The knat7 T-DNA insertion mutants have thinner vessel element walls and xylary fibers, and thicker interfascicular fiber walls in inflorescence stems, relative to wild-type （WT）. KNAT7 over- expression plants exhibited opposite effects. Glycosyl linkage and sugar composition analyses revealed lower xylan levels in knat7 inflorescence stems, relative to WT; a finding supported by labeling of inflorescence walls with xylan-specific antibodies. The knat7 loss-of-function mutants had lower transcript levels of the xylan biosynthetic genes IRX9, IRX10, and FRAS, whereas KNAT7 overexpression plants had higher mRNA levels for IRX9, IRX10, IRX14L, and FRA8. Electrophoretic mobility shift assays indicated that KNAT7 binds to the IRX9 promoter. These results support the hypothesis that KNAT7 positively regulates xylan biosynthesis.

The CELLULOSE-SYNTHASE LIKE C （CSLC） Family of Barley Includes Members that Are Integral Membrane Proteins Targeted to the Plasma Membrane

The CELLULOSE SYNTHASE-LIKE C （CSLC） family is an ancient lineage within the CELLULOSE SYNTHASE/CELLULOSE SYNTHASE-LIKE （CESA/CSL） polysaccharide synthase superfamily that is thought to have arisen before the divergence of mosses and vascular plants. As studies in the flowering plant Arabidopsis have suggested synthesis of the （1,4）-β-glucan backbone of xyloglucan （XyG）, a wall polysaccharide that tethers adjacent cellulose microfibrils to each other, as a probable function for the CSLCs, CSLC function was investigated in barley （Hordeum vulgate L.）, a species with low amounts of XyG in its walls. Four barley CSLCgenes were identified （designated HvCSLC1-4）. Phylogenetic analysis reveals three well supported clades of CSLCs in flowering plants, with barley having representatives in two of these clades. The four barley CSLCs were expressed in various tissues, with in situ PCR detecting transcripts in all cell types of the coleoptile and root, including cells with primary and secondary cell walls. Co-expression analysis showed that HvCSLC3 was coordinately expressed with putative XyG xylosyltransferase genes. Both immuno-EM and membrane fractionation showed that HvCSLC2 was located in the plasma membrane of barley suspension-cultured cells and was not in internal membranes such as endoplasmic reticulum or Golgi apparatus. Based on our current knowledge of the sub-cellular locations of polysaccharide synthesis, we conclude that the CSLC family probably contains more than one type of polysaccharide synthase.

Plant glycosylphosphatidylinositol anchored proteins at the plasma membrane-cell wall nexus

Approximately 1% of plant proteins are predicted to be post-translationally modified with a glycosylphospha- tidylinositol （GPI） anchor that tethers the polypeptide to the outer leaflet of the plasma membrane. Whereas the synthesis and structure of GPI anchors is largely conserved across eukaryotes, the repertoire of functional domains present in the GPl-anchored proteome has diverged substantially. In plants, this includes a large fraction of the GPl-anchored proteome being further modified with plant-specific arabinogalactan （AG） O-glycans. The impor- tance of the GPl-anchored proteome to plant development is underscored by the fact that GPI biosynthetic null mutants exhibit embryo lethality. Mutations in genes encoding specific GPl-anchored proteins （GAPs） further supports their contribution to diverse biological processes, occurring at the interface of the plasma membrane and cell wall, including signaling, cell wall metabolism, cell wall polymer cross-linking, and plasmodesmatal transport. Here, we review the literature concerning plant GPl-anchored proteins, in the context of their potential to act as molecular hubs that mediate interactions between the plasma membrane and the cell wall, and their potential to transduce the signal into the protoplast and, thereby, activate signal transduction pathways.

Role of UDP-Glucuronic Acid Decarboxylase in Xylan Biosynthesis in Arabidopsis

UDP-xylose （UDP-Xyl） is the Xyl donor used in the synthesis of major plant cell-wall polysaccharides such as xylan （as a backbone-chain monosaccharide） and xyloglucan （as a branching monosaccharide）. The biosynthesis of UDP-Xyl from UDP-glucuronic acid （UDP-GIcA） is irreversibly catalyzed by UDP- glucuronic acid decarboxylase （UXS）. Until now, little has been known about the physiological roles of UXS in plants. Here, we report that AtUXS1, AtUXS2, and AtUXS4 are located in the Golgi apparatus whereas AtUXS3, AtUXS5, and AtUXS6 are located in the cytosoh Although all six single AtUXS T-DNA mu- tants and the uxsl usx2 uxs4 triple mutant show no obvious phenotype, the uxs3 uxs5 uxs6 triple mutant has an irregular xylem phenotype. Monosaccharide analysis showed that Xyl levels decreased in uxs3 uxs5 uxs6 and linkage analysis confirmed that the xylan content in uxs3 xus5 uxs6 declined, indicating that UDP-Xyl from cytosol AtUXS participates in xylan synthesis. Gel-permeation chromatography showed that the molecular weight of non-cellulosic polysaccharides in the triple mutants, mainly composed of xylans, is lower than that in the wild type, suggesting an effect on the elongation of the xylan backbone. Upon saccharification treatment stems of the uxs3 uxs5 uxs6 triple mutants released monosaccharides with a higher efficiency than those of the wild type. Taken together, our results indicate that the cytosol UXS plays a more important role than the Golgi-localized UXS in xylan biosynthesis.

A Phytochrome B-PIF4-MYC2/MYC4 module inhibits secondary cell wall thickening in response to shaded light

Secondary cell walls(SCWs)in stem cells provide mechanical strength and structural support for growth.SCW thickening varies under different light conditions.Our previous study revealed that blue light enhances SCW thickening through the redundant function of MYC2 and MYC4 directed by CRYPTOCHROME1(CRY1)signaling in fiber cells of the Arabidopsis inflorescence stem.In this study,we find that the Arabidopsis PHYTOCHROME B mutant phyB displays thinner SCWs in stem fibers,but thicker SCWs are deposited in the PHYTOCHROME INTERACTING FACTOR(PIF)quadruple mutant pif1pif3pif4pif5(pifq).The shaded light condition with a low ratio of red to far-red light inhibits stem SCW thickening.PIF4 interacts with MYC2 and MYC4 to affect their localization in nuclei,and this interaction results in inhibition of the MYCs’transactivation activity on the NST1 promoter.Genetic evidence shows that regulation of SCW thickening by PIFs is dependent on MYC2/MYC4 function.Together,the results of this study reveal a PHYB-PIF4-MYC2/MYC4 module that inhibits SCW thickening in fiber cells of the Arabidopsis stem.

The Cellulose Synthases Are Cargo of the TPLATE Adaptor Complex

Dear Editor Clathrin-mediated endocytosis （CME） is an evolutionary conserved mechanism by which plasma membrane （PM）-based cargo proteins are recognized by adaptor protein complexes and internalized. Apart from the canonical adaptor complex, AP-2, plant cells rely on the TPLATE complex （TPC） to execute CME （Gadeyne et al., 2014）. FT160100218, DP110100410）, the Ministry of Education, Culture, Sports, Science, and Technology of Japan （24114003, 15H04382, and 17K19412）, the European Research Council （ERC grant 682436）, the IRRTF-RNC （no. 501892） and a USA National Science Foundation CAREER Award.

Integrative Multi-omics Analyses of Barley Rootzones under Salinity Stress Reveal Two Distinctive Salt Tolerance Mechanisms

The mechanisms underlying rootzone-localized responses to salinity during early stages of barley development remain elusive.In this study,we performed the analyses of multi-root-omes(transcriptomes,metabolomes,and lipidomes)of a domesticated barley cultivar(Clipper)and a landrace(Sahara)that maintain and restrict seedling root growth under salt stress,respectively.Novel generalized linear models were designed to determine differentially expressed genes(DEGs)and abundant metabolites(DAMs)specific to salt treatments,genotypes,or rootzones(meristematic Z1,elongation Z2,and maturation Z3).Based on pathway over-representation of the DEGs and DAMs,phenylpropanoid biosynthesis is the most statistically enriched biological pathway among all salinity responses observed.Together with histological evidence,an intense salt-induced lignin impregnation was found only at stelic cell wall of Clipper Z2,compared with a unique elevation of suberin deposition across Sahara Z2.This suggests two differential salt-induced modulations of apoplastic flow between the genotypes.Based on the global correlation network of the DEGs and DAMs,callose deposition that potentially adjusted symplastic flow in roots was almost independent of salinity in rootzones of Clipper,and was markedly decreased in Sahara.Taken together,we propose two distinctive salt tolerance mechanisms in Clipper(growth-sustaining)and Sahara(salt-shielding),providing important clues for improving crop plasticity to cope with deteriorating global soil salinization.