Sporobolus stapfianus transcriptome: Insights into the unique adaptations of the resurrection grasses to the dehydration stress

Sporobolus stapfianus is a desiccation tolerant (DT) grass and a member of the Poaceae family alongside prominent crop and forage species. Despite the worldwide distribution of this family, most of its species are vulnerable to water loss within their vegetative tissues. As a DT species, S. stapfianus, could, therefore, serve as a model species for identifying the molecular changes that enabled such a rare occurrence of the DT phenotype in resurrection grasses and the implications of such a unique adaptation for agriculture. A comprehensive gene expression profiling was performed in plants subjected to a dehydration/rehydration cycle using NimbleGen microarrays hybridization method. Our results showed that most transcripts were high in the hydrated state of S. stapfianus leaf tissues and that minor dehydration (> 60% relative water content; RWC) did not induce most transcripts, but did repress photosynthetic activity, which show the importance of curtailing the production of toxic elements to the DT phenotype. It took a loss of 40% RWC for induction of most transcripts. This shows that this species is pre-equipped to deal with mild dehydration, but requires stress-induced activation mechanisms to prepare for desiccation. In agreement with our transcriptomic data, a global metabolic analysis conducted in this species has shown that most metabolites accumulate to their highest levels below 45% RWC, which suggests the importance of those late stages of dehydration in preparing resurrection grasses for desiccation and for early stages of rehydration. In most cases, a 12-h rehydration was sufficient to reinstate pre-stress expression levels, which shows that only partial damage occurred during drying. Unlike during dehydration, our metabolomic data profiled after rehydration showed that there is no clear correlation between gene expression and metabolic abundance, which suggests that most of the compounds that are produced during rehydration are quickly utilized in active metabolism of restoration. The findings of the paper show that S. stapfianus is primed to respond to mild dehydration, although severe dehydration require inducible response, with 40-30% RWC being the peak of gene expression. As for photosynthesis, this species cease its photosynthetic activity even at high water levels (85% RWC) alleviating the need to activate antioxidants activity during mild dehydration. Overall design: Total RNA was extracted from the grass, Sporobolus stapfianus leaf tissues at six hydration levels (3.0, 2.0, 1.5, 1.0, 0.75, and 0.50 g water/ g tissue) as well as at 12 and 24 h after rehydration. Each treatment was conducted in triplicates; making a total of 24 samples. Each chip measures the expresion level of 50,690 genes with each gene model represented by 7x60 mer probes.

Sporobolus stapfianus，一种耐旱（DT）型禾本科植物，与众多重要作物和牧草物种同属一科。尽管该科植物在全球范围内分布广泛，但其中大部分物种在生长组织中易受水分丧失的威胁。作为耐旱物种，S. stapfianus 因此可成为研究复活草类植物中耐旱表型罕见出现的分子变化以及这种独特适应性对农业影响的模型物种。本研究采用 NimbleGen 微阵列杂交技术，对经历脱水/复水周期的植物进行了全面的基因表达谱分析。结果显示，S. stapfianus 叶组织在含水量较高时转录本水平较高，轻微脱水（> 60% 相对含水量；RWC）并未诱导大多数转录本，但确实抑制了光合作用，这表明减少有毒物质产生对耐旱表型的重要性。当 RWC 损失 40% 时，大多数转录本被诱导。这表明该物种天生具有应对轻度脱水的适应性，但需要应激诱导的激活机制来为脱水做准备。与转录组数据一致，对该物种进行的全局代谢分析显示，大多数代谢物在 RWC 低于 45% 时积累到最高水平，这表明脱水后期对复活草类植物进入脱水状态和复水早期阶段的重要性。在大多数情况下，12 小时的复水足以恢复应激前的表达水平，这表明干燥过程中仅发生了部分损伤。与脱水过程不同，我们在复水后进行的代谢组数据分析显示，基因表达与代谢丰度之间没有明显的相关性，这表明在复水过程中产生的多数化合物在恢复的活跃代谢中迅速被利用。论文的研究发现表明，S. stapfianus 预先准备好对轻度脱水作出反应，尽管严重脱水需要可诱导的响应，40-30% RWC 为基因表达的高峰。至于光合作用，该物种即使在高水分水平（85% RWC）下也会停止光合作用，从而减轻了在轻度脱水期间激活抗氧化剂活动的需求。总体设计：从六个水分含量水平（3.0、2.0、1.5、1.0、0.75 和 0.50 g 水每 g 组织）以及复水后 12 小时和 24 小时的 Sporobolus stapfianus 禾本科植物叶片组织中提取总 RNA。每个处理重复三次，共计 24 个样本。每个芯片测量 50,690 个基因的表达水平，每个基因模型由 7x60 甲基探针表示。