Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas - UPV, ES-46022 Valencia, Spain.
Plant J. 2009 Nov;60(4):575-88. doi: 10.1111/j.1365-313X.2009.03981.x. Epub 2009 Jul 16.
Abscisic acid (ABA) is a key phytohormone involved in adaption to environmental stress and regulation of plant development. Clade A protein phosphatases type 2C (PP2Cs), such as HAB1, are key negative regulators of ABA signaling in Arabidopsis. To obtain further insight into regulation of HAB1 function by ABA, we have screened for HAB1-interacting partners using a yeast two-hybrid approach. Three proteins were identified, PYL5, PYL6 and PYL8, which belong to a 14-member subfamily of the Bet v1-like superfamily. HAB1-PYL5 interaction was confirmed using BiFC and co-immunoprecipitation assays. PYL5 over-expression led to a globally enhanced response to ABA, in contrast to the opposite phenotype reported for HAB1-over-expressing plants. F(2) plants that over-expressed both HAB1 and PYL5 showed an enhanced response to ABA, indicating that PYL5 antagonizes HAB1 function. PYL5 and other members of its protein family inhibited HAB1, ABI1 and ABI2 phosphatase activity in an ABA-dependent manner. Isothermal titration calorimetry revealed saturable binding of (+)ABA to PYL5, with K(d) values of 1.1 mum or 38 nm in the absence or presence of the PP2C catalytic core of HAB1, respectively. Our work indicates that PYL5 is a cytosolic and nuclear ABA receptor that activates ABA signaling through direct inhibition of clade A PP2Cs. Moreover, we show that enhanced resistance to drought can be obtained through PYL5-mediated inhibition of clade A PP2Cs.
脱落酸（ABA）是一种参与环境胁迫适应和植物发育调控的关键植物激素。类 A 蛋白磷酸酶 2C（PP2C），如 HAB1，是拟南芥 ABA 信号的关键负调控因子。为了进一步了解 ABA 对 HAB1 功能的调节，我们使用酵母双杂交方法筛选了 HAB1 相互作用伙伴。鉴定了三个蛋白质，PYL5、PYL6 和 PYL8，它们属于 Bet v1 样超家族的 14 个成员亚家族。使用 BiFC 和共免疫沉淀实验证实了 HAB1-PYL5 相互作用。PYL5 的过表达导致对 ABA 的整体反应增强，与报道的 HAB1 过表达植物的相反表型形成对比。过表达 HAB1 和 PYL5 的 F2 植物对 ABA 的反应增强，表明 PYL5 拮抗 HAB1 功能。PYL5 和其蛋白质家族的其他成员以 ABA 依赖的方式抑制 HAB1、ABI1 和 ABI2 磷酸酶活性。等温滴定量热法显示 (+)ABA 与 PYL5 的结合是饱和的，在不存在或存在 HAB1 的 PP2C 催化核心的情况下，Kd 值分别为 1.1 mum 或 38nm。我们的工作表明，PYL5 是一种细胞质和核 ABA 受体，通过直接抑制类 A PP2C 激活 ABA 信号。此外，我们表明，通过 PYL5 介导的抑制类 A PP2C，可以获得对干旱的增强抗性。
