Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA.
Proc Natl Acad Sci U S A. 2009 Dec 15;106(50):21419-24. doi: 10.1073/pnas.0910601106. Epub 2009 Dec 2.
The plant hormone abscisic acid (ABA) serves as a physiological monitor to assess the water status of plants and, under drought conditions, induces stomatal pore closure by activating specific ion channels, such as a slow-anion channel (SLAC1) that, in turn, mediate ion efflux from the guard cells. Earlier genetic analyses uncovered a protein kinase (OST1) and several 2C-type phosphatases, as respective positive and negative regulators of ABA-induced stomatal closure. Here we show that the OST1 kinase interacts with the SLAC1 anion channel, leading to its activation via phosphorylation. PP2CA, one of the PP2C phosphatase family members acts in an opposing manner and inhibits the activity of SLAC1 by two mechanisms: (1) direct interaction with SLAC1 itself, and (2) physical interaction with OSTI leading to inhibition of the kinase independently of phosphatase activity. The results suggest that ABA signaling is mediated by a physical interaction chain consisting of several components, including a PP2C member, SnRK2-type kinase (OST1), and an ion channel, SLAC1, to regulate stomatal movements. The findings are in keeping with a paradigm in which a protein kinase-phosphatase pair interacts physically with a target protein to couple a signal with a specific response.
植物激素脱落酸 (ABA) 作为一种生理监测物，评估植物的水分状况，在干旱条件下，通过激活特定的离子通道，如缓慢阴离子通道 (SLAC1)，从而介导 guard cells 中的离子外流，诱导气孔关闭。早期的遗传分析发现了一种蛋白激酶 (OST1) 和几种 2C 型磷酸酶，分别作为 ABA 诱导气孔关闭的正、负调节因子。本文展示了 OST1 激酶与 SLAC1 阴离子通道相互作用，通过磷酸化使其激活。PP2C 磷酸酶家族成员之一的 PP2CA 以相反的方式起作用，并通过两种机制抑制 SLAC1 的活性：（1）直接与 SLAC1 相互作用，（2）与 OST1 的物理相互作用，独立于磷酸酶活性抑制激酶。结果表明，ABA 信号转导是通过包括 PP2C 成员、SnRK2 型激酶 (OST1) 和离子通道 SLAC1 在内的几个组成部分的物理相互作用链介导的，以调节气孔运动。这一发现与一种模式一致，即蛋白激酶-磷酸酶对与靶蛋白相互作用，将信号与特定反应偶联。
