Transcriptional, metabolic, physiological and developmental responses of switchgrass to phosphorus limitation

Knowing how switchgrass (Panicum virgatum L.) responds and adapts to phosphorus (P)-limitation will aid efforts to optimize P acquisition and use in this species for sustainable biomass production. This integrative study investigated the impacts of mild, moderate, and severe P-stress on genome transcription and whole-plant metabolism, physiology and development in switchgrass. P-limitation reduced overall plant growth, increased root/shoot ratio, increased root branching at moderate P-stress, and decreased root diameter with increased density and length of root hairs at severe P-stress. RNA-seq analysis revealed thousands of genes that were differentially expressed under moderate and severe P-stress in roots and/or shoots compared to P-replete plants, with many stress-induced genes involved in transcriptional and other forms of regulation, primary and secondary metabolism, transport, and other processes involved in P-acquisition and homeostasis. Amongst the latter were multiple miRNA399 genes and putative targets of these. Metabolite profiling showed that levels of most sugars and sugar alcohols decreased with increasing P stress, while organic and amino acids increased under mild and moderate P-stress in shoots and roots, although this trend reversed under severe P-stress, especially in shoots. Comparative gene expression profiling analysis of RNA-seq data from switchgrass plants grown under optimal nutritional conditions or with different phosphorus limitation regimes (mild, moderate and severe) for four weeks.

解析柳枝稷（switchgrass，Panicum virgatum L.）对磷（P）限制的响应与适应机制，可为优化该物种的磷获取与利用效率、实现生物质可持续生产提供理论支撑。本综合研究探讨了轻度、中度与重度磷胁迫对柳枝稷基因组转录、全株代谢、生理及生长发育的影响。磷限制会抑制植株整体生长，提高根冠比；中度磷胁迫下根系分支增多，重度磷胁迫下根径减小，同时根毛密度与长度均有所提升。RNA-seq分析显示，相较于磷充足植株，中度与重度磷胁迫下根系和/或地上组织中存在数千个差异表达基因，其中大量胁迫诱导基因参与转录调控及其他调控途径、初级与次级代谢、物质转运，以及其他与磷获取和稳态维持相关的生物学过程，其中不乏多个miRNA399基因及其推定靶标。代谢组分析结果显示，随着磷胁迫程度加剧，多数糖类与糖醇类物质的含量呈下降趋势；而在轻度与中度磷胁迫下，植株地上组织与根系中的有机酸及氨基酸含量均有所上升，但重度磷胁迫下该趋势发生逆转，尤其在地上组织中表现显著。本研究同时针对生长于最优营养条件，或施加轻度、中度、重度磷限制处理共四周的柳枝稷植株的RNA-seq数据，开展了比较基因表达谱分析。