小立碗藓水分胁迫应答中通过miRNA66调控ABA平衡的分子机制

Drought is a major factor limiting plant growth and crop productivity. Multiple mechanisms in responding to water stress have been developed during the evolution of plants from aquatic to terrestrial environments and abscisic acid (ABA) acts as a key signaling molecular. When plants sense the stress, ABA signal transduction are triggered, leading to the establishment of a new homeostasis of downstream gene expression and eventually corresponding stress responses. Researches on ABA receptors and signaling have achieved significant breakthrough within recent years. However, the precise modulating mechanism of ABA metabolism is still not clear. microRNAs (miRNA) have broad functions in eukaryotic gene regulation. However, until now only a few reports suggested the involvement of miRNAs in regulating ABA synthesis or metabolism-related gene expressions. We have many years of experience in the research of Physmitrella patens stress responses and have constructed a regulation network of Physcomitrella dehydration-related miRNA. Mutants of candidate miRNAs have been generated and their phenotypes under water stress or ABA treatment been tested. A Physcomitrella specific miRNA (named as miRNA 66), which could be dramatically and rapidly induced by ABA or osmotic stress, was identified. The mirna66 knock-out mutant is highly resistant to dehydration treatment. While the over-expression transgenic plant exhibits opposite phenotypes. Moreover, we observed alteration of transcriptional levels of several key genes in ABA biosynthesis or metabolism pathways in mirna66 mutants. In this project, molecular and cellular biological techniques will be employed to investigate the role of miRNA66 in regulating ABA biosynthesis and metabolism in Physcomitrella water stress responses. And our work might shed light in dehydration resistance-related crop breeding.

干旱严重影响作物产量。植物从水生向陆生发展历程中，面对可能的水分亏缺演化出多种适应机制，脱落酸ABA是其关键信号分子。植物感受到胁迫后，通过ABA信号途径调控下游基因的时空表达，继而呈现出相应胁迫应答。ABA受体与信号转导的分子机制比较清晰，但ABA合成与代谢的精确调控机制不清。miRNAs在真核生物的基因表达调控中具广泛作用，但尚无其参与ABA合成与代谢调控的报道。我们研究小立碗藓逆境胁迫应答机制多年，建立了与干旱相关的miRNAs调控网络，构建了多个候选miRNAs敲除突变体，选出一个受渗透胁迫与ABA快速诱导的小立碗藓特异miRNA66，其缺失突变体抗旱，而过表达者则否；ABA合成与代谢关键基因的转录水平在miRNA66敲除突变体中均有对应变化。我们将采用分子、细胞生物学等技术，深入解析miRNA66在小立碗藓水分胁迫应答中对ABA合成与代谢的精确调控机制，为作物抗旱育种提供基础。

脱落酸（ABA）被认为是介导植物中非生物反应，包括的极端干旱应答，的中心节点。 ABA生物合成和核心信号组分介导的胁迫响应机制在陆生植物中是高度保守的。然而，对于基部陆地植物，即陆生植物祖先的现存近亲中，ABA参与极端干旱应答反应的分子机制目前尚不清楚。本项目通过对模式植物小立碗藓的研究，发现一个物种特异性的miR1023a-PpDRP介导的ABA信号级联，与经典的，ABI3介导的ABA信号转导平行并相互调控。 Micro RNA1023a通过其靶分子PpDRP，影响ABA生物合成中的限速度酶PpZEP / ABA1和PpNECD来调节ABA稳态。同时，极端干旱处理可诱导ABA积累， 并提高miR1023a和PpDRP的表达。这就成为一条反馈回路，精确调节极端干旱反应中的内源ABA水平。由于miR1023a的消失，PpDRP的直系同源基因丧失了在维管植物中的脱水耐受的作用。我们的研究结果为依赖ABA的极端干旱耐受机制，以及陆地植物进化和植物中ABA信号通路的进化提供了新的补充。