Sweet sorghum and Miscanthus：Two potential dedicated bioenergy crops in China

Among the potential non-food energy crops,the sugar-rich C4 grass sweet sorghum and the biomass-rich Miscanthus are increasingly considered as two leading candidates.Here,we outline the biological traits of these energy crops for largescale production in China.We also review recent progress on understanding of plant cell wall composition and wall polymer features of both plant species from large populations that affect both biomass enzymatic digestibility and ethanol conversion rates under various pretreatment conditions.We finally propose genetic approaches to enhance biomass production,enzymatic digestibility and sugar-ethanol conversion efficiency of the energy crops.

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.

The connection of cytoskeletal network with plasma membrane and the cell wall

The cell wall provides external support of the plant cells, while the cytoskeletons including the microtubules and the actin filaments constitute an internal framework. The cytoskeletons contribute to the cell wall biosynthesis by spatially and temporarily regulating the transportation and deposition of cell wall components. This tight control is achieved by the dynamic behavior of the cytoskeletons, but also through the tethering of these structures to the plasma membrane. This tethering may also extend beyond the plasma membrane and impact on the cell wall, possibly in the form of a feedback loop. In this review, we discuss the linking components between the cytoskeletons and the plasma membrane, and/or the cell wall. We also discuss the prospective roles of these components in cell wall biosyn- thesis and modifications, and aim to provide a platform for further studies in this field.

Method for hull-less barley transformation and manipulation of grain mixed-linkage beta-glucan

Hull-less barley is increasingly offering scope for breeding grains with improved characteristics for human nutrition; however, recalcitrance of hull-less cultivars to transformation has limited the use of these varieties. To overcome this limitation, we sought to develop an effective transformation system for hull-less barley using the cultivar Torrens. Torrens yielded a transformation efficiency of 1.8%, using a modified Agrobacterium transformation method. This method was used to over-express genes encoding synthases for the important dietary fiber component, 0,3;1,4）-β-glucan （mixed-linkage glucan）, primarily present in starchy endosperm cell walls. Over-expression of the HvCslF6 gene, driven by an endosperm-specific promoter, produced lines where mixed-linkage glucan content increased on average by 45%, peaking at 70% in some lines, with smaller increases in transgenic HvCsIH1 grain. Transgenic HvCslF6 lines displayed alterations where grain had a darker color, were more easily crushed than wild type and were smaller. This was associated with an enlarged cavity in the central endosperm and changes in cell morphology, including aleurone and sub-aleurone cells. This work provides proof-of-concept evidence that mixed-linkage glucan content in hull-less barley grain can be increased by over-expression of the HvCslF6 gene, but also indicates that hull-less cultivars may be more sensitive to attempts to modify cell wall composition.

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.

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.

T-DNA-Induced Chromosomal Translocations in feronia and anxur2 Mutants Reveal Implications for the Mechanism of Collapsed Pollen Due to Chromosomal Rearrangements

Dear Editor, Approximately every fifth Arabidopsis T-DNA inser- tion line contains chromosomal translocations caused by the inserted T-DNA （Clark and Krysan, 2010）. Albeit broad use of T-DNA lines for mutant analysis, little is known about the consequences of these chromosomal rearrangements and only a few studies describe chromosomal aberrations in the mutant lines. While plant growth in general is not affected by such chromosomal translocations, defects in gametophyte development have been observed in lines that are heterozygous for the T-DNA insertion （Ray et al., 1997; Curtis et al., 2009）.

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.

植物初生细胞壁到次生细胞壁合成的转化及调控(英文)

次生细胞壁的合成是植物的重要发育过程之一,它不仅是植物细胞实现某些特定功能所必需的,也是植物维持其形态的物质基础.与初生细胞壁不同的是次生壁的合成开始于细胞停止生长后,而初生壁的合成则是伴随细胞生长同时进行的.因此,由初生壁合成到次生壁合成的转化意味着植物体内需要进行一次重要的代谢调整.两种细胞壁合成的转化需要一系列胞内生理生化活动的协同合作.这些活动包括:激素调控、转录调控、转录后调控以及代谢通量的重分布等.本文概述了初生壁合成到次生壁合成转化所涉及的转录和激素调控,并且指出了我们对相关代谢网络认知的不足.此外,本文还对现有的可用于研究该转化的工具系统进行了讨论.