Plant Cell|中国科学院西双版纳热带植物园胡彦如实验室在ABA介导种子萌发研究中取得新进展
种子萌发和萌发后生长需要多种内在信号和环境信号的精确协调。植物激素脱落酸(ABA)抑制这些过程在拟南芥和昼夜节律时钟有助于调节 ABA 信号。然而，昼夜节律钟介导的 ABA 信号转导的分子机制仍然很大程度上是未知的。在这里，我们发现核心生物钟蛋白反应调节蛋白5(PRR5)和 PRR7在物理上与 ABA 信号转导的关键转录因子脱落酸不敏感蛋白5(ABI5)相关。
PRR5和 PRR7在种子萌发过程中对 ABA 信号的相关调节起着积极的作用。同时干扰 PRR5和 PRR7使发芽种子对 ABA 敏感性降低，而 PRR5的过表达增强 ABA 信号抑制种子发芽。与此一致的是，若干 aba 应答基因的表达被 PRR 蛋白上调。遗传分析表明，PRR5主要依赖 ABI5启动 ABA 信号转导。
图11.种子萌发过程中ABI5和PRR蛋白相互作用调节ABA信号的简化模型
进一步的机制研究表明 PRR5激活 ABI5的转录功能而不影响其稳定性。总的来说，我们的研究结果表明，这些 PRR 蛋白与 ABI5协同作用，激活种子萌发过程中的 ABA 反应，从而提供了 ABA 信号和昼夜节律时钟如何通过涉及 ABI5和中枢生物钟成分的转录复合物直接整合的机制性理解。
Abstract
Seed germination and postgerminative growth require the precise coordination of multiple intrinsic and environmental signals. The phytohormone abscisic acid (ABA) suppresses these processes in Arabidopsis thaliana and the circadian clock contributes to the regulation of ABA signaling. However, the molecular mechanism underlying circadian clock-mediated ABA signaling remains largely unknown. Here, we found that the core circadian clock proteins PSEUDO-RESPONSE REGULATOR5 (PRR5) and PRR7 physically associate with ABSCISIC ACID INSENSITIVE5 (ABI5), a crucial transcription factor of ABA signaling. PRR5 and PRR7 positively modulate ABA signaling redundantly during seed germination. Disrupting PRR5 and PRR7 simultaneously rendered germinating seeds hyposensitive to ABA, whereas overexpression of PRR5 enhanced ABA signaling to inhibit seed germination. Consistent with this, the expression of several ABA-responsive genes is upregulated by PRR proteins. Genetic analysis demonstrated that PRR5 promotes ABA signaling mainly dependently on ABI5. Further mechanistic investigation revealed that PRR5 stimulates the transcriptional function of ABI5 without affecting its stability. Collectively, our results indicate that these PRR proteins function synergistically with ABI5 to activate ABA responses during seed germination, thus providing a mechanistic understanding of how ABA signaling and the circadian clock are directly integrated through a transcriptional complex involving ABI5 and central circadian clock components.
https://doi.org/10.1093/plcell/koab168
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