J Integr Plant Biol ›› 2020, Vol. 62 ›› Issue (5): 690-701.DOI: 10.1111/jipb.12824

• Plant-biotic Interactions • Previous Articles     Next Articles

BAK1‐mediated phosphorylation of canonical G protein alpha during flagellin signaling in Arabidopsis

Jiao Xue, Ben-Qiang Gong, Xinran Yao, Xiangjuan Huang and Jian-Feng Li*   

  1. 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

    These authors contributed equally to this work.
    *Correspondence:
    Email: Jian-Feng Li (lijfeng3@mail.sysu.edu.cn)
  • Received:2019-03-08 Accepted:2019-05-04 Online:2019-05-14 Published:2020-05-01

Abstract:

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 Thr19 upon flg22 elicitation. Interestingly, flg22 could not induce phosphorylation of GPA1T19A and GPA1T19D, suggesting that the dynamic Thr19 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 GPA1T19A 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.

Canonical G protein alpha (GPA1) is thought to play a negligible role in Arabidopsis immunity. Here we show genetic and phosphoproteomic evidence that GPA1 positively regulates immunity. Bacterial flagellin can enhance GPA1 phosphorylation through the co‐receptor BAK1, where dynamic phosphorylation of Thr19 is indispensable for GPA1 to respond to flagellin.
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