Osmotic stress and abscisic acid (ABA) signaling are important for plant growth and abiotic stress resistance. Activation of osmotic and ABA signaling downstream of the PYL-type ABA receptors requires the release of SnRK2 protein kinases from the inhibition imposed by PP2Cs. PP2Cs are core negative regulators that constantly interact with and inhibit SnRK2s, but how osmotic signaling breaks the PP2C inhibition of SnRK2s remains unclear. Here, we report that an Arabidopsis receptor-like cytoplasmic kinase, BIK1, releases PP2C-mediated inhibition of SnRK2.6 via phosphorylation regulation. The dominant abi1-1 ABA-signaling mutation (G180D) disrupts PYL-PP2C interactions and disables PYL-initiated release of SnRK2s; in contrast, BIK1 releases abi1-1-mediated inhibition of SnRK2.6. BIK1 interacts with and phosphorylates SnRK2.6 at two tyrosine residues, which are critical for SnRK2.6 activation and function. Phosphorylation of the two tyrosine residues may affect the docking of the tryptophan "lock" of PP2C into SnRK2.6. Moreover, the bik1 mutant is defective in SnRK2 activation, stress-responsive gene expression, ABA accumulation, growth maintenance, and water loss under osmotic stress. Our findings uncover the critical role of BIK1 in releasing PP2C-mediated inhibition of SnRK2s under osmotic stress.

中文翻译：

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渗透信号转导通过受体样细胞质激酶 BIK1 释放 PP2C 介导的拟南芥 SnRK2 抑制。


渗透胁迫和脱落酸 （ABA） 信号传导对植物生长和非生物胁迫抗性很重要。PYL 型 ABA 受体下游渗透和 ABA 信号传导的激活需要从 PP2C 施加的抑制中释放 SnRK2 蛋白激酶。PP2C 是不断与 SnRK2 相互作用并抑制 SnRK2 的核心负调节因子，但渗透信号如何打破 SnRK2 的 PP2C 抑制仍不清楚。在这里，我们报道了拟南芥受体样细胞质激酶 BIK1 通过磷酸化调节释放 PP2C 介导的 SnRK2.6 抑制。显性 abi1-1 ABA 信号突变 （G180D） 破坏 PYL-PP2C 相互作用并禁用 PYL 启动的 SnRK2 释放;相反，BIK1 释放 abi1-1 介导的 SnRK2.6 抑制。BIK1 与两个酪氨酸残基相互作用并磷酸化 SnRK2.6，这对 SnRK2.6 的激活和功能至关重要。两个酪氨酸残基的磷酸化可能会影响 PP2C 的色氨酸“锁”与 SnRK2.6 的对接。此外，bik1 突变体在渗透胁迫下的 SnRK2 激活、应激反应基因表达、ABA 积累、生长维持和水分流失方面存在缺陷。我们的研究结果揭示了 BIK1 在渗透应激下释放 PP2C 介导的 SnRK2s 抑制中的关键作用。