茉莉素信号调控植物复氧应答的功能及分子机理

Hypoxia is one of the most important abiotic stresses that affect the growth and yield of plants. Current evidence suggests that significant different strategies are involved in plant responses to hypoxia and reoxygenation, a process by immediate exposure of plants to oxygen following hypoxic stress. Within the past several years, our understanding into the molecular and biochemical mechanisms of hypoxia sensing and signaling in plants has been greatly forwarded. However, the molecular basis of plant responses to reoxygenation remains to be further investigated. Our preliminary data show that in Arabidopsis thaliana, the endogenous contents of JAs are rapidly accumulated and the transcripts of JAs biosynthesis genes are inducible by reoxygenation. Moreover, the exogenous application of MeJA improves the hypoxic tolerance of wild-type Arabidopsis, while the deficient mutants in both JAs biosynthesis and signaling are highly sensitive to hypoxia. Further, transcriptomic and bioinformatic analyses indicate that the involvement of JAs signaling in reoxygenation response is likely linked to the modulation of the expression of VTC1 and GSH1, two genes encode rate-limiting enzymes in the ascorbate and glutathione synthesis pathways, by the key transcription factor MYC2. The increased levels of such antioxidants may contribute to the alleviation of oxidative damages caused by reoxygenation, which therefore improves the plant’s survival upon hypoxia. By genetic and biochemical approaches, we further intend to elucidate the mechanism of how JAs signaling interacts with the antioxidant synthesis pathways to regulate reoxygenation response in Arabidopsis.

低氧是影响植物生长与作物产量最重要的非生物胁迫之一。研究表明，植物在低氧胁迫下和在复氧过程中采取完全不同的应答策略。近年来，对于植物感受和响应低氧胁迫的分子机制研究取得了许多重要进展，但对植物如何响应复氧反应的作用机理了解非常有限。前期研究显示，野生型拟南芥内源茉莉素(JAs)的含量在植物复氧过程中迅速积累，且JAs合成相关基因受复氧诱导表达。同时，外源施加MeJA可以显著改善植物的低氧耐受性，而JAs合成和信号转导缺失突变体则对低氧胁迫非常敏感。转录组和生物信息学分析发现，JAs信号作用于植物复氧反应，可能是通过转录因子MYC2调控抗坏血酸和谷胱甘肽合成限速酶基因VTC1和GSH1的表达，增强抗氧化系统，从而减轻植物细胞的氧化损伤。本项目拟通过遗传学与生物化学手段，深入解析JAs参与植物复氧反应的生理功能，及JAs介导的植物复氧反应与抗氧化系统相互作用的分子机理。

长时间淹水胁迫会导致植物细胞遭受缺氧，影响植物的生长发育。而在水淹退去后重新暴露在氧气中的复氧过程又会使植物产生大量活性氧，造成氧化胁迫，进一步威胁植物的生存。目前，植物低氧感知和信号传导机制研究已取得很大进展，但植物如何应对去水淹后的复氧反应仍然不清楚。本项目研究发现，拟南芥的复氧应答过程中茉莉素（JA）的含量快速积累，且JA生物合成相关基因的转录水平显著上调，表明JA可能是植物复氧响应的关键信号分子。表型分析表明，外源施加茉莉酸甲酯（MeJA）能够显著提高野生型拟南芥对复氧胁迫的耐受性，而茉莉酸生物合成缺陷和信号传导缺陷突变体对复氧胁迫异常敏感。进一步研究发现，JA通路关键转录因子MYC2基因的过表达能够增强植物对低氧后复氧胁迫的耐受性，而myc2敲除突变体对复氧反应的敏感性增加，表明MYC2在JA介导的复氧反应中起着关键的调节作用。转录组学和生化分析表明，MYC2蛋白与抗坏血酸合成酶限速酶基因（VTCs）和谷胱甘肽合成酶基因（GSHs）家族成员的启动子相互作用，且转录激活其基因表达。遗传分析发现，过表达VTC1和GSH1的转基因植物能显著互补myc2-2突变体对缺氧后复氧反应的超敏感表型，进一步证实了JA信号通路和抗氧化途径的遗传调控关系。本研究揭示了茉莉酸诱导的抗氧化物的积累可以减轻植物复氧胁迫引起的氧化损伤，提高植物淹水后的存活率。综上所述，本项目研究成果阐明了茉莉素信号与抗氧化途径的相互作用以调节植物复氧反应的生物学功能与作用机理，研究结果对于深入理解植物响应低氧和复氧环境的分子机制具有重要的科学意义。