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.

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.

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.

Root-Specific Transcript Profiling of Contrasting Rice Genotypes in Response to Salinity Stress

Elevated salinity imposes osmotic and ion toxicity stresses on living cells and requires a multitude of responses in order to enable plant survival. Building on earlier work profiling transcript levels in rice （Oryza sativa） shoots of FL478, a salt-tolerant indica recombinant inbred line, and IR29, a salt-sensitive cultivar, transcript levels were compared in roots of these two accessions as well as in the roots of two additional salt-tolerant indica genotypes, the landrace Pokkali and the recombinant inbred line IR63731. The aim of this study was to compare transcripts in the sensitive and the tolerant lines in order to identify genes likely to be involved in plant salinity tolerance, rather than in responses to salinity perse. Transcript profiles of several gene families with known links to salinity tolerance are described （e.g. HKTs, NHXs）. The putative function of a set of genes identified through their salt responsiveness, transcript levels, and/or chro- mosomal location （i.e. underneath QTLs for salinity tolerance） is also discussed. Finally, the parental origin of the Saltol region in FL478 is further investigated. Overall, the dataset presented appears to be robust and it seems likely that this system could provide a reliable strategy for the discovery of novel genes involved in salinity tolerance.

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.

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）.

The variable codons of H5N1 avian influenza A virus haemagglutinin genes

We investigated the selection pressures on the haemagglutinin genes of H5N1 avian influenza viruses using fixed effects likelihood models. We found evidence of positive selection in the sequences from isolates from 1997 to 2007, except viruses from 2000. The haemagglutinin sequences of viruses from southeast Asia, Hong Kong and China's Mainland were the most polymorphic and had similar nonsyn-onymous profiles. Some sites were positively selected in viruses from most regions and a few of these sites displayed different amino acid patterns. Selection appeared to produce different outcomes in vi-ruses from Europe, Africa and Russia and from different host types. One position was found to be positively selected for human isolates only. Although the functions of some positively selected posi-tions are unknown, our analysis provided evidence of different temporal, spatial and host adaptations for H5N1 avian influenza viruses.

Mutation of a Gene in the Fungus Leptosphaeria maculans Allows Increased Frequency of Penetration of Stomatal Apertures of Arabidopsis thaliana

Leptosphaeria maculans, a pathogen of Brassica napus, is unable to invade most wild-type accessions of Arabidopsis thaliana, although several mutants are susceptible. The infection pathway of L. maculans via a non-invasive inoculation method on A. thaliana Imsl （undefined）, pmr4-1 （defective in callose deposition）, and pen1-1 and pen2-1 （defective in non-host responses to several pathogens） mutants is described. On wild types Col-0 and Ler-0, hyphae are generally arrested at stomatal apertures. A T-DNA insertional mutant of L. maculans （A22） that penetrates stomatal apertures of Col-0 and Ler-0 five to seven times more often than the wild-type isolate is described. The higher penetration frequency of isolate A22 is associated with an increased hypersensitive response, which includes callose deposition. Com- plementation analysis showed that the phenotype of this isolate is due to T-DNA insertion in an intronless gene denoted as ipa （increased penetration on A rabidopsis）. This gene is predicted to encode a protein of 702 amino acids with best matches to hypothetical proteins in other filamentous ascomycetes. The ipa gene is expressed in the wild-type isolate at low levels in culture and during infection of A. thaliana and B. napus.

H5N1禽流感病毒血凝素基因密码子的变异

应用固定效应似然模型研究了作用于H5N1禽流感病毒血凝素基因的选择压力．研究发现，除2000年以外，1997—2007年，H5N1病毒的血凝素基因都受到正选择压力的作用．东南亚、中国香港和中国大陆的血凝素序列氨基酸多态性最复杂，并且具有相似的非同义突变模式．大部分地区的H5N1病毒血凝素基因的一些位点受到正选择压力的影响，并且其中一些位点在不同地区的病毒中具有不同的氨基酸模式．另外，正选择压力对分离自欧洲、非洲和俄罗斯以及不同宿主类型的H5N1病毒产生了不同的影响．一个位点只在取自人类的病毒中被发现受到正选择压力的影响．尽管一些受到正选择压力的位点的功能尚不清楚，但是本文的分析提供了H5N1禽流感病毒适应不同时间、地点和寄主的遗传证据．