Guangdong Provincial Key Laboratory of Plant Resources, State Key Laboratory of Biocontrol, MOE Key Laboratory of Gene Function and Regulation, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China.
J Integr Plant Biol. 2020 May;62(5):690-701. doi: 10.1111/jipb.12824. Epub 2019 Oct 17.
Heterotrimeric G proteins consisting of Gα, Gβ and Gγ are conserved signaling hubs in eukaryotes. Without analogs to canonical animal G protein-coupled receptors, plant cells are thought to use RGS1 and a yet unknown mechanism to regulate the activity of Gα. Meanwhile, the exact role of canonical Gα in plant innate immunity remains controversial. Here, we report multiple immune deficiencies in the null allele of Arabidopsis Gα (GPA1) in response to bacterial flg22 elicitor, clarifying a positive regulatory role of GPA1 in flg22 signaling. We also detect overall increased phosphorylation of GPA1 but reduced phosphorylation at Thr upon flg22 elicitation. Interestingly, flg22 could not induce phosphorylation of GPA1 and GPA1 , suggesting that the dynamic Thr phosphorylation is required for GPA1 to respond to flg22. Moreover, flg22-induced GPA1 phosphorylation is largely abolished in the absence of BAK1 in vivo, and BAK1 could phosphorylate GPA1 but not GPA1 in vitro at the phosphorylation sites identified in vivo, suggesting BAK1 is likely the kinase for GPA1 phosphorylation in response to flg22. Furthermore, the T19A mutation could promote flg22-induced association, rather than dissociation, between GPA1 and RGS1. Taken together, our findings shed new insights into the function and regulation of GPA1 in Arabidopsis defense signaling.
三聚体 G 蛋白由 Gα、Gβ 和 Gγ组成，是真核生物中保守的信号枢纽。由于没有类似于经典动物 G 蛋白偶联受体的同源物，植物细胞被认为使用 RGS1 和一种未知的机制来调节 Gα 的活性。同时，经典 Gα 在植物先天免疫中的确切作用仍存在争议。在这里，我们报告了拟南芥 Gα（GPA1）缺失突变体对细菌 flg22 诱导剂的多种免疫缺陷，阐明了 GPA1 在 flg22 信号中的正向调节作用。我们还检测到 flg22 诱导后 GPA1 的整体磷酸化增加，但 Thr 磷酸化减少。有趣的是，flg22 不能诱导 GPA1 和 GPA1 的磷酸化，表明动态 Thr 磷酸化是 GPA1 响应 flg22 的必要条件。此外，体内缺乏 BAK1 时，flg22 诱导的 GPA1 磷酸化在很大程度上被消除，并且 BAK1 可以在体内鉴定的磷酸化位点处体外磷酸化 GPA1，但不能磷酸化 GPA1，表明 BAK1 可能是 flg22 诱导 GPA1 磷酸化的激酶。此外，T19A 突变可以促进 flg22 诱导的 GPA1 与 RGS1 之间的结合，而不是解离。总之，我们的研究结果为 GPA1 在拟南芥防御信号中的功能和调节提供了新的见解。
