J Integr Plant Biol. ›› 2021, Vol. 63 ›› Issue (2): 327-339.DOI: 10.1111/jipb.13007

• Research Articles • Previous Articles     Next Articles

Arabidopsis E3 ligase KEG associates with and ubiquitinates MKK4 and MKK5 to regulate plant immunity

Chenyang Gao1,2,3 , Pengwei Sun2,3, Wei Wang1 and Dingzhong Tang1*   

  1. 1State Key Laboratory of Ecological Control of Fujian‐Taiwan Crop Pests, Key Laboratory of Ministry of Education for Genetics, Breeding and Multiple Utilization of Crops, Plant Immunity Center, Fujian Agriculture and Forestry University, Fuzhou 350002, China
    2Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences, Beijing 100101, China
    3College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China

    *Correspondence: Dingzhong Tang (dztang@genetics.ac.cn)
  • Received:2020-07-10 Accepted:2020-08-31 Online:2020-09-02 Published:2021-02-01

Abstract: Mitogen‐activated protein kinase (MAPK) cascades are highly conserved signaling modules that regulate plant immune responses. The Arabidopsis thaliana Raf‐like MAPK kinase kinase ENHANCED DISEASE RESISTANCE1 (EDR1) is a key negative regulator of plant immunity that affects the protein levels of MKK4 and MKK5, two important MAPK cascade members, but the underlying mechanism is poorly understood. Here, genome‐wide phosphorylation analysis demonstrated that the E3 ligase KEEP ON GOING (KEG) is phosphorylated in the edr1 mutant but not the wild type, suggesting that EDR1 negatively affects KEG phosphorylation. The identified phosphorylation sites in KEG appear to be important for its accumulation. The keg‐4 mutant, a previously identified edr1 suppressor, enhances susceptibility to the powdery mildew pathogen Golovinomyces cichoracearum. In addition, MKK4 and MKK5 protein levels are reduced in the keg‐4 mutant. Furthermore, we demonstrate that MKK4 and MKK5 associate with full‐length KEG, but not with truncated KEG‐RK or KEG‐RKA, and that KEG ubiquitinates and mediates the degradation of MKK4 and MKK5. Taken together, these results indicate that MKK4 and MKK5 protein levels are regulated by KEG via ubiquitination, uncovering a mechanism by which plants fine‐tune immune responses by regulating the homeostasis of key MAPK cascade members via ubiquitination and degradation.

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