Ubiquitination is a major mechanism of eukaryotic posttranslational protein turnover that has been implicated in abscisic acid (ABA)-mediated drought stress response. Here, we isolated T-DNA insertion mutant lines in which ABA-insensitive RING protein 5 (AtAIRP5) was suppressed, resulting in hyposensitive ABA-mediated germination compared to wild-type Arabidopsis (Arabidopsis thaliana) plants. A homology search revealed that AtAIRP5 is identical to gibberellin (GA) receptor RING E3 ubiquitin (Ub) ligase (GARU), which downregulates GA signaling by degrading the GA receptor GID1, and thus AtAIRP5 was renamed AtAIRP5/GARU. The atairp5/garu knockout progeny were impaired in ABA-dependent stomatal closure and were markedly more susceptible to drought stress than wild-type plants, indicating a positive role for AtAIRP5/GARU in the ABA-mediated drought stress response. Yeast two-hybrid, pull-down, target ubiquitination, and in vitro and in planta degradation assays identified serine carboxypeptidase-like1 (AtSCPL1), which belongs to the clade 1A AtSCPL family, as a ubiquitinated target protein of AtAIRP5/GARU. atscpl1 single and atairp5/garu-1 atscpl1-2 double mutant plants were more tolerant to drought stress than wild-type plants in an ABA-dependent manner, suggesting that AtSCPL1 is genetically downstream of AtAIRP5/GARU. After drought treatment, the endogenous ABA levels in atscpl1 and atairp5/garu-1 atscpl1-2 mutant leaves were higher than those in wild-type and atairp5/garu leaves. Overall, our results suggest that AtAIRP5/GARU RING E3 Ub ligase functions as a positive regulator of the ABA-mediated drought response by promoting the degradation of AtSCPL1.

中文翻译：

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E3 连接酶 AtAIRP5/GARU 通过刺激丝氨酸羧肽酶-LIKE1 转换来调节干旱胁迫反应。

泛素化是真核生物翻译后蛋白转换的主要机制，与脱落酸 (ABA) 介导的干旱胁迫反应有关。在这里，我们分离出 T-DNA 插入突变体系，其中 ABA 不敏感环蛋白 5 (AtAIRP5) 被抑制，导致与野生型拟南芥 (Arabidopsis thaliana) 植物相比，ABA 介导的发芽不敏感。同源性搜索显示 AtAIRP5 与赤霉素 (GA) 受体 RING E3 泛素 (Ub) 连接酶 (GARU) 相同，后者通过降解 GA 受体 GID1 来下调 GA 信号，因此 AtAIRP5 更名为 AtAIRP5/GARU。atairp5/garu 敲除后代在 ABA 依赖性气孔关闭中受损，并且比野生型植物更容易受到干旱胁迫，表明 AtAIRP5/GARU 在 ABA 介导的干旱胁迫反应中具有积极作用。酵母双杂交、pull-down、靶标泛素化以及体外和植物内降解测定鉴定了丝氨酸羧肽酶样 1 (AtSCPL1)，它属于进化枝 1A AtSCPL 家族，是 AtAIRP5/GARU 的泛素化靶蛋白。atscpl1 单突变体和 atairp5/garu-1 atscpl1-2 双突变体植物比野生型植物以 ABA 依赖性方式更耐受干旱胁迫，这表明 AtSCPL1 在基因上位于 AtAIRP5/GARU 下游。干旱处理后，atscpl1 和atairp5/garu-1 atscpl1-2 突变体叶片的内源ABA 水平高于野生型和atairp5/garu 叶片。全面的，