Cyclic GMP (cGMP) is an important regulator in eukaryotes, and cGMP-dependent protein kinase (PKG) plays a key role in perceiving cellular cGMP in diverse physiological processes in animals. However, the molecular identity, property, and function of PKG in plants remain elusive. In this study, we have identified PKG from plants and characterized its role in mediating the gibberellin (GA) response in rice (Oryza sativa). PKGs from plants are structurally unique with an additional type 2C protein phosphatase domain. Rice PKG possesses both protein kinase and phosphatase activities, and cGMP stimulates its kinase activity but inhibits its phosphatase activity. One of PKG's targets is GAMYB, a transcription factor in GA signaling, and the dual activities of PKG catalyze the reversible phosphorylation of GAMYB at Ser6 and modulate the nucleocytoplasmic distribution of GAMYB in response to GA. Loss of PKG impeded the nuclear localization of GAMYB and abolished GAMYB function in the GA response, leading to defects in GA-induced seed germination, internode elongation, and pollen viability. In addition to GAMYB, PKG has multiple potential targets and thus has broad effects, particularly in the salt stress response.

中文翻译：

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植物 cGMP 依赖性蛋白激酶的双重活性及其在赤霉素信号传导和盐胁迫中的作用。

环鸟苷酸 (cGMP) 是真核生物中的重要调节因子，环鸟苷酸 (cGMP) 依赖性蛋白激酶 (PKG) 在动物多种生理过程中感知细胞环鸟苷酸 (cGMP) 中发挥着关键作用。然而，植物中 PKG 的分子特性、性质和功能仍然难以捉摸。在这项研究中，我们从植物中鉴定出了 PKG，并表征了其在介导水稻 (Oryza sativa) 赤霉素 (GA) 反应中的作用。来自植物的 PKG 结构独特，具有额外的 2C 型蛋白磷酸酶结构域。大米PKG同时具有蛋白激酶和磷酸酶活性，cGMP刺激其激酶活性但抑制其磷酸酶活性。PKG 的目标之一是 GAMYB，GA 信号传导中的转录因子，PKG 的双重活性催化 GAMYB Ser6 位点的可逆磷酸化，并响应 GA 调节 GAMYB 的核质分布。PKG 的缺失阻碍了 GAMYB 的核定位，并废除了 GA 反应中的 GAMYB 功能，导致 GA 诱导的种子萌发、节间伸长和花粉活力缺陷。除了 GAMYB 之外，PKG 还具有多个潜在靶点，因此具有广泛的作用，特别是在盐胁迫反应中。