• Drought severely affects crop growth and yields. Stomatal regulation plays an important role in plant response to drought stress. Light-activated plasma membrane-localized proton ATPase (PM H⁺-ATPase) mainly promoted the stomatal opening. Abscisic acid (ABA) plays a dominant role in the stomatal closure during drought stress. It is not clear how PM H⁺-ATPase is involved in the regulation of ABA-induced stomatal closure.
• We found that a CALCIUM-DEPENDENT PROTEIN KINASE RELATED KINASE 1 (ZmCRK1), and its mutant zmcrk1 exhibited slow water loss in detached leaves, high-survival rate after drought stress, and sensitivity to stomatal closure induced by ABA. The ZmCRK1 overexpression lines are opposite.
• ZmCRK1 interacted with the maize PM H⁺-ATPase ZmMHA2. ZmCRK1 phosphorylated ZmMHA2 at the Ser-901 and inhibited its proton pump activity. ZmCRK1 overexpression lines and zmmha2 mutants had low H⁺-ATPase activity, resulting in impaired ABA-induced H⁺ efflux.
• Taken together, our study indicates that ZmCRK1 negatively regulates maize drought stress response by inhibiting the activity of ZmMHA2. Reducing the expression level of ZmCRK1 has the potential to reduce yield losses under water deficiency.

中文翻译：

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ZmCRK1 通过磷酸化质膜 H+-ATP 酶 ZmMHA2 负向调节玉米对干旱胁迫的反应

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  干旱严重影响作物生长和产量。气孔调节在植物对干旱胁迫的响应中起着重要作用。光激活质膜定位质子 ATP 酶 （PM H⁺-ATP 酶） 主要促进气孔开放。脱落酸 （ABA） 在干旱胁迫期间气孔关闭中起主导作用。目前尚不清楚 PM H⁺-ATP 酶如何参与 ABA 诱导的气孔关闭的调节。
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  我们发现钙依赖性蛋白激酶相关激酶 1 （ZmCRK1） 及其突变体 zmcrk1 在脱落的叶片中表现出缓慢的水分流失、干旱胁迫后高存活率以及对 ABA 诱导的气孔关闭敏感。ZmCRK1 过表达线相反。
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  ZmCRK1 与玉米 PM H⁺-ATP 酶 ZmMHA2 相互作用。ZmCRK1 在 Ser-901 位点磷酸化 ZmMHA2 并抑制其质子泵活性。ZmCRK1 过表达系和 zmmha2 突变体具有低 H⁺-ATP 酶活性，导致 ABA 诱导的 H⁺ 外排受损。
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  综上所述，我们的研究表明 ZmCRK1 通过抑制 ZmMHA2 的活性负向调节玉米干旱胁迫响应。降低 ZmCRK1 的表达水平有可能减少缺水情况下的产量损失。