Abscisic acid regulates stomatal production by imprinting a SnRK2 kinase–mediated phosphocode on the master regulator SPEECHLESS

背景回顾：Stomata, the epidermal pores for gas exchange between plants and the atmosphere, are the major sites of water loss. During water shortage, plants limit the formation of new stoma via the phytohormone abscisic acid (ABA) to conserve water. 

提出问题：However, how ABA suppresses stomatal production is largely unknown. 

主要发现：Here, we demonstrate that three core SnRK2 kinases of ABA signaling inhibit the initiation and proliferation of the stomatal precursors in Arabidopsis. 

结果1-SnRK2s磷酸化SPCH：We show that the SnRK2s function within the precursors and directly phosphorylate SPEECHLESS (SPCH), the master transcription factor for stomatal initiation. 

结果2-SPCH上的磷酸位点：We identify specific SPCH residues targeted by the SnRK2s, which mediate the ABA/drought-induced suppression of SPCH and stomatal production. 

结论：This SnRK2-specific SPCH phosphocode connects stomatal development with ABA/drought signals and enables the independent control of this key water conservation response. Our work also highlights how distinct signaling activities can be specifically encoded on a master regulator to modulate developmental plasticity.

Model of the effect of ABA on stomatal development.

 摘 要 

气孔，位于植物表皮上用于交换气体的特殊结构，也是植物水分丢失的主要途径。在水分存储过程中，植物会通过植物激素脱落酸（ABA）来限制新气孔的形成，从而保存水分。但是，ABA如何抑制气孔的形成，这在很大程度上还是未知的。本文中，作者发现拟南芥ABA信号转导通路上3个核心SnRK2激酶抑制了气孔前体的起始和增殖。SnRK2s在气孔前体中发挥功能，直接磷酸化调控气孔起始的关键转录因子SPCH蛋白。作者进一步鉴定到了SPCH蛋白上被SnRK2磷酸化的氨基酸残基，介导了ABA/干旱诱导的SPCH和气孔形成抑制。这一SnRK2特异性的SPCH蛋白磷酸密码将气孔发育与ABA/干旱信号连接在一起，并使得植物中这一关键的水保存响应得以独立控制。本文的工作同时还揭示了不同的信号转导活性如何被编码于关键调控子上，以介导植物的发育可塑性。

** On Sun Lau **