半干旱黄土丘陵沟壑区柳枝稷（Panicum virgatum）的生物质形成

为深入认识半干旱黄土丘陵沟壑区引种能源植物柳枝稷生物质生产的开发潜力及其约束机制,调查了农田、植丛尺度上早熟和晚熟柳枝稷年度生命周期内生物量累积、分株建成动态,以及土壤水分供求平衡过程。研究发现,植丛尺度早熟柳枝稷抽穗比例近100％,分株生殖发生大小阈值依赖基本丧失,高度大小分布近似正态,种群内光资源竞争强度明显弱化,与晚熟类型形成明显差异。农田尺度晚熟柳枝稷生物质产量可以达到15t／hm^2,高出早熟类型近1倍,但是其立地80～400cm土层的含水量稳定在7％以下,土壤干旱已经发生,早期干旱胁迫导致的生长停滞,以及生长中后期的成片倒伏现象在两年的观测周期内连续出现。早熟柳枝稷立地则形成相对稳定的白草、柳枝稷复合优势植被结构,深层土壤水分含量稳定在10％以上,实现了跨年度的土壤水分供求平衡。植丛尺度的生物质形成在一定程度上取决于分株生殖发生的大小依赖程度和分株间竞争关系格局,基于植丛尺度普遍的生殖发生和明显弱化的光资源竞争,早熟柳枝稷表现出更为高效的生物质形成机制。农田尺度晚熟柳枝稷尽管在雨热同步期的降水资源利用效率上存在明显比较优势,但是在降水资源利用分配策略和效应上,早熟柳枝稷表现出了综合的生态适宜性优势。保证雨热同步期降水资源利用和保蓄的平衡,是半干旱黄土丘陵沟壑区生物质生产应该遵循的基本原则之一。     

Proteome profile of the endomembrane of developing coleoptiles from switchgrass (Panicum virgatum)

The cost‐effective production of biofuels from lignocellulosic material will likely require manipulation of plant biomass, specifically cell walls. The North American native prairie grass Panicum virgatum (switchgrass) is seen as a potential biofuel crop with an array of genetic resources currently being developed. We have characterized the endomembrane proteome of switchgrass coleoptiles to provide additional information to the switchgrass community. In total, we identified 1750 unique proteins from two biological replicates. These data have been deposited in the ProteomeXchange with the identifier PXD001351 ( http://proteomecentral.proteomexchange.org/dataset/PXD001351 ).     

A simplified protocol for genetic transformation of switchgrass (Panicum virgatum L.)

The increasing interest in renewable energy has attracted more research attention on biofuels. In order to generate sustainable amount of biomass feedstock from dedicated biofuel crops such as switchgrass they need to be genetically improved. Genetic transformation is one of the techniques to achieve this goal. The aim of our study was to devise a simplified protocol for switchgrass genetic transformation. We have used NB(0) as the basal medium and mature seeds of the cultivar Alamo as the starting material. The nutrient medium used and scutellum-derived callus are fashioned after rice genetic transformation protocols. We obtained friable calluses, which were similar to the type II calluses in other monocotyledonous species. Calluses were amenable for Agrobacterium-mediated genetic transformation with at least 6?% transformation efficiency. The concentration of hygromycin was optimized for successful selection of transgenic calluses. The Green Fluorescent Protein gene was used to monitor and demonstrate successful genetic transformation. Compared to the previously published methods for genetic transformation of switchgrass, our protocol is simpler and equally efficient. KEY MESSAGE: An efficient, simplified switchgrass genetic transformation method with NB(0) basal medium and mature seeds as inoculum was developed. The appropriate concentrations of hormones and selection agent are described.     

Nanoparticle titanium dioxide affects the growth and microRNA expression of switchgrass (Panicum virgatum)

Nanoparticle TiO₂ is a common chemical used in daily life. As increasing usage of TiO₂, it is becoming a potentially dangerous contaminant to the environment. However, the impact of TiO₂ is not well understood. In this paper, switchgrass was employed to investigate the impacts of nanoparticle TiO₂ on plant growth and development as well as the potential impact on the expression of microRNAs (miRNAs). TiO₂ significantly affected switchgrass seed generation as well as plant growth and development in a dose-dependent manner. Particularly, TiO₂ significantly inhibited root development. miRNA expressions were also significantly altered. Nanoparticle TiO₂ may regulate plant development through controlling the expression of certain miRNAs. Among the 16 tested miRNAs, the expression of some miRNAs, such as miR390 and miR399 was increased with increasing TiO₂ concentrations; the expression of some miRNAs, such as miR169 was decreased with increasing TiO₂ concentrations; the other miRNAs show different expression patterns.     

MicroRNA expression analysis in the cellulosic biofuel crop switchgrass (Panicum virgatum) under abiotic stress

Switchgrass has increasingly been recognized as a dedicated biofuel crop for its broad adaptation to marginal lands and high biomass. However, little is known about the basic biology and the regulatory mechanisms of gene expression in switchgrass, particularly under stress conditions. In this study, we investigated the effect of salt and drought stress on switchgrass germination, growth and the expression of small regulatory RNAs. The results indicate that salt stress had a gradual but significant negative effect on switchgrass growth and development. The germination rate was significantly decreased from 82% for control to 36% under 1% NaCl treatment. However, drought stress had little effect on the germination rate but had a significant effect on the growth of switchgrass under the severest salinity stress. Both salt and drought stresses altered the expression pattern of miRNAs in a dose-dependent manner. However, each miRNA responded to drought stress in a different pattern. Salt and drought stress changed the expression level of miRNAs mainly from 0.9-fold up-regulation to 0.7-fold down-regulation. miRNAs were less sensitive to drought treatment than salinity treatment, as evidenced by the narrow fold change in expression levels. Although the range of change in expression level of miRNAs was similar under salt and drought stress, no miRNAs displayed significant change in expression level under all tested salt conditions. Two miRNAs, miR156 and miR162, showed significantly change in expression level under high drought stress. This suggests that miR156 and miR162 may attribute to the adaption of switchgrass to drought stress and are good candidates for improving switchgrass as a biofuel crop by transgenic technology.     

Genomic diversity in switchgrass (Panicum virgatum): from the continental scale to a dune landscape

Connecting broad-scale patterns of genetic variation and population structure to genetic diversity on a landscape is a key step towards understanding historical processes of migration and adaptation. New genomic approaches can be used to increase the resolution of phylogeographic studies while reducing locus sampling effects and circumventing ascertainment bias. Here, we use a novel approach based on high-throughput sequencing to characterize genetic diversity in complete chloroplast genomes and >10,000 nuclear loci in switchgrass, at continental and landscape scales. Switchgrass is a North American tallgrass species, which is widely used in conservation and perennial biomass production, and shows strong ecotypic adaptation and population structure across the continental range. We sequenced 40.9 billion base pairs from 24 individuals from across the species' range and 20 individuals from the Indiana Dunes. Analysis of plastome sequence revealed 203 variable SNP sites that define eight haplogroups, which are differentiated by 4-127 SNPs and confirmed by patterns of indel variation. These include three deeply divergent haplogroups, which correspond to the previously described lowland-upland ecotypic split and a novel upland haplogroup split that dates to the mid-Pleistocene. Most of the plastome haplogroup diversity present in the northern switchgrass range, including in the Indiana Dunes, originated in the mid- or upper Pleistocene prior to the most recent postglacial recolonization. Furthermore, a recently colonized landscape feature (approximately 150 ya) in the Indiana Dunes contains several deeply divergent upland haplogroups. Nuclear markers also support a deep lowland-upland split, followed by limited gene flow, and show extensive gene flow in the local population of the Indiana Dunes.     

Internode structure and cell wall composition in maturing tillers of switchgrass (Panicum virgatum. L)

This work examined cell composition gradients in maturing tillers of switchgrass (Panicum virgatum L.) with the aim of developing baseline information on this important forage and biomass crop. Flowering tillers were collected from plants raised from seeds in a greenhouse and field, harvested at soil level and separated into internodes beginning with the node subtending the peduncle. Internodes were analyzed using microscopy, by fiber digestion, high-performance liquid chromatography and by gas chromatography-mass spectrometry to obtain anatomical and compositional data. Microscopy demonstrated the development and maturation of cortical fibers which eventually became confluent with the fiber sheath surrounding vascular bundles in the lower internodes. Detergent fiber analysis indicated increasing cellulose and lignin contents and decreases in cell solubles and hemicelluloses with increasing distance of the internodes from the top of the plant. Soluble phenolics were greatest in amounts and complexity in top internodes. The lower internodes contained greater levels of wall-bound phenolic acids, principally as 4-coumarate and ferulate.     

Habitat restoration and native grass conservation: a case study of switchgrass (Panicum virgatum)

Switchgrass (Panicum virgatum) has been planted extensively for habitat restoration across the United States, such as with the Conservation Reserve Program (CRP). However, genetic profiles of these populations have never been studied nor compared with those of remnant prairies or cultivars. In this study, we sampled 16 CRP and 17 prairie populations across eastern Kansas. We assessed ploidy levels of all populations and compared genetic diversity and structure of 10 prairies, 10 CRP areas, and 5 standard cultivars, using nine simple sequence repeat (SSR) DNA markers. All CRP and prairie populations were octaploid (8x), except two prairies with both hexaploid (6x) and octaploid (8x) individuals. Based on the results of SSR analyses, there were no significant differences between CRP and prairie populations in genetic diversity, and 94% of total variation was partitioned within populations. Similarities among prairie and CRP populations were also observed in Bayesian clustering algorithms and principal coordinate analysis, suggesting that they had similar genetic compositions. In addition, positive spatial autocorrelations were detected up to 42 and 46 km among prairie and among CRP populations, respectively. To conclude, the CRP and prairie populations shared similar genetic profiles. However, remnant prairies still harbored unique genotypes and a high level of genetic diversity, highlighting the importance of seed sources for restoration efforts, that is using local wild seeds or cultivars from the same geographical region. A popular tetraploid (4x) cultivar known as “Kanlow” was genetically distinct from the prairie populations and therefore is not recommended for habitat restoration in this region.