Adaptation Versus Senescence In Rice: Early Signalling Events Play A Role In Inducing Specificity And Tolerance To Salinity
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Salinity tolerance is a complex trait and, despite many efforts to obtain rice plants resistant to salt, few results have been achieved since a deeper understanding of the tolerance mechanisms is still needed. We used imaging of photosynthetic parameters, ion analysis and transcriptomic approaches to unveil differences between two rice varieties differing in salt sensitivity. Moreover, we analysed H2O2 production in roots, using a fluorescent probe, and the ensuing gene regulation. Transcriptomic analyses conducted in tolerant plants supported the set-up of an adaptive program consisting of allocating sodium preferentially to roots, restricting it to the oldest leaves and activating regulatory mechanisms of photosynthesis in new leaves. As a consequence, plants resumed growth even under prolonged salt stress. By contrast, in the susceptible variety, RNA profiling unveiled a mis-targeted response, leading to senescence and cell death. In roots of tolerant plants, an increase in H2O2 was observed as early as 5 minutes after treatment. Consequently, the expression of genes involved in perception, signal transduction and response to salt were induced at earlier times when compared to susceptible plant roots. Our results demonstrate that a prompt H2O2 signalling in roots participates to a coordinated response resulting in adaptation instead of senescence in salt treated rice plants.
盐胁迫耐受性是一类复杂性状。尽管学界已开展诸多研究以培育耐盐水稻植株，但目前仍未取得显著突破，核心原因在于对植物耐盐耐受机制的深层认知仍存在不足。本研究通过光合参数成像、离子组分析与转录组学技术，解析了两个盐敏感性存在显著差异的水稻品种间的生理与分子差异。此外，本研究利用荧光探针检测了根系内过氧化氢（H₂O₂）的产生水平，并分析了伴随发生的基因调控变化。对耐盐水稻植株的转录组分析结果显示，其启动了一套适应性调控程序：优先将钠离子分配至根系、限制钠离子向老叶转运，并激活新叶中的光合调控机制。借此，即便在长期盐胁迫环境下，水稻植株仍可恢复正常生长。与之形成鲜明对比的是，盐敏感品种的转录谱分析显示其应答机制存在靶向偏差，最终引发叶片衰老与细胞死亡。在耐盐品种的根系中，盐胁迫处理后仅5分钟即可检测到过氧化氢水平的显著升高。因此，与盐敏感品种的根系相比，耐盐品种根系中参与盐胁迫感知、信号转导及胁迫应答的基因更早被诱导表达。本研究结果证实，根系内快速启动的过氧化氢信号通路参与构建了一套协同应答机制，最终使盐胁迫处理的水稻植株走向适应性存活而非衰老死亡。
