Department of Biological Sciences, Sookmyung Women's University, Seoul 140-742, Republic of Korea.
Department of Systems Biology, Yonsei University, Seoul 120-749, Republic of Korea.
Mol Plant. 2016 Mar 7;9(3):447-460. doi: 10.1016/j.molp.2015.12.014. Epub 2015 Dec 24.
Stomatal movements are critical in regulating gas exchange for photosynthesis and water balance between plant tissues and the atmosphere. The plant hormone abscisic acid (ABA) plays key roles in regulating stomatal closure under various abiotic stresses. In this study, we revealed a novel role of BAK1 in guard cell ABA signaling. We found that the brassinosteroid (BR) signaling mutant bak1 lost more water than wild-type plants and showed ABA insensitivity in stomatal closure. ABA-induced OST1 expression and reactive oxygen species (ROS) production were also impaired in bak1. Unlike direct treatment with H2O2, overexpression of OST1 did not completely rescue the insensitivity of bak1 to ABA. We demonstrated that BAK1 forms a complex with OST1 near the plasma membrane and that the BAK1/OST1 complex is increased in response to ABA in planta. Brassinolide, the most active BR, exerted a negative effect on ABA-induced formation of the BAK1/OST1 complex and OST1 expression. Moreover, we found that BAK1 and ABI1 oppositely regulate OST1 phosphorylation in vitro, and that ABI1 interacts with BAK1 and inhibits the interaction of BAK1 and OST1. Taken together, our results suggest that BAK1 regulates ABA-induced stomatal closure in guard cells.
气孔运动对于光合作用和植物组织与大气之间的水分平衡的气体交换至关重要。植物激素脱落酸（ABA）在各种非生物胁迫下调节气孔关闭中起关键作用。在这项研究中，我们揭示了 BAK1 在保卫细胞 ABA 信号转导中的新作用。我们发现，油菜素内酯（BR）信号突变体 bak1 失去的水分比野生型植物多，并且在气孔关闭中表现出对 ABA 的不敏感性。ABA 诱导的 OST1 表达和活性氧（ROS）产生也在 bak1 中受到损害。与直接用 H2O2 处理不同，过表达 OST1 并不能完全挽救 bak1 对 ABA 的不敏感性。我们证明 BAK1 在质膜附近与 OST1 形成复合物，并且该 BAK1/OST1 复合物在体内响应 ABA 而增加。油菜素内酯，最活跃的 BR，对 ABA 诱导的 BAK1/OST1 复合物形成和 OST1 表达产生负效应。此外，我们发现 BAK1 和 ABI1 在体外相反地调节 OST1 的磷酸化，并且 ABI1 与 BAK1 相互作用并抑制 BAK1 和 OST1 的相互作用。总之，我们的结果表明 BAK1 调节保卫细胞中 ABA 诱导的气孔关闭。
