Institut des Sciences du Végétal, Centre National de la Recherche Scientifique, UPR2355, 1 Avenue de la Terrasse, Bât. 23, 91198 Gif-sur-Yvette, France.
Mol Plant. 2011 Jul;4(4):562-80. doi: 10.1093/mp/ssr055. Epub 2011 Jul 10.
The year 2009 marked a real turnaround in our understanding of the mode of abscisic acid (ABA) action. Nearly 25 years had elapsed since the first biochemical detection of ABA-binding proteins in the plasmalemma of Vicia guard cells was reported. This recent--and laudable--achievement is owed largely to the discovery of the soluble ABA receptors whose major interacting proteins happen to be some of the most well-established components of earliest steps in ABA signaling. These soluble receptors, with the double name of PYRABACTIN RESISTANCE (PYR) or REGULATORY COMPONENT OF ABA RECEPTOR (RCAR), are a family of Arabidopsis proteins of about 150-200 amino acids that share a conserved START domain. The ABA signal transduction circuitry under non-stress conditions is muted by the clade A protein phosphatases 2C (PP2C) (notably HAB1, ABI1, and ABI2). During the initial steps of ABA signaling, the binding of the hormone to the receptor induces a conformational change in the latter that allows it to sequester the PP2Cs. This excludes them from the negative regulation of the downstream ABA-activated kinases (OST1/SnRK2.6/SRK2E, SnRK2.2, and SnRK2.3), thus unleashing the pathway by freeing them to phosphorylate downstream targets that now include several b-ZIP transcription factors, ion channels (SLAC1, KAT1), and a NADPH oxidase (AtrbohF). The discovery of this family of soluble receptors and the rich insight already gained from structural studies of their complexes with different isoforms of ABA, PP2C, and the synthetic agonist pyrabactin lay the foundation towards rational design of chemical switches that can bolster drought hardiness in plants.
2009 年标志着我们对脱落酸（ABA）作用模式的理解发生了真正的转变。自首次报道 Vicia guard 细胞质膜中 ABA 结合蛋白的生化检测以来，已经过去了近 25 年。这一最近的——值得称赞的——成就主要归功于可溶性 ABA 受体的发现，其主要相互作用蛋白恰好是 ABA 信号转导早期步骤中最成熟的一些组成部分。这些可溶性受体，具有 PYRABACTIN RESISTANCE（PYR）或 ABA RECEPTOR REGULATORY COMPONENT（RCAR）的双重名称，是大约 150-200 个氨基酸的拟南芥蛋白家族，它们共享一个保守的 START 结构域。在非胁迫条件下，ABA 信号转导电路被 clade A 蛋白磷酸酶 2C（PP2C）（特别是 HAB1、ABI1 和 ABI2）沉默。在 ABA 信号转导的初始步骤中，激素与受体的结合诱导后者构象发生变化，从而使其能够隔离 PP2C。这将它们排除在下游 ABA 激活激酶（OST1/SnRK2.6/SRK2E、SnRK2.2 和 SnRK2.3）的负调控之外，从而通过释放它们来磷酸化下游靶标来释放途径，现在包括几个 b-ZIP 转录因子、离子通道（SLAC1、KAT1）和 NADPH 氧化酶（AtrbohF）。可溶性受体家族的发现以及从其与不同 ABA、PP2C 同工型和合成激动剂 pyrabactin 的复合物的结构研究中获得的丰富见解，为合理设计可以增强植物耐旱性的化学开关奠定了基础。
