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Poster

Session: Session 1 Presenting Authors at Posters (Odds)

P-057 - Molecular mechanisms of MAP kinase-mediated activation and Xanthomonas XopP-mediated inhibition of PUB44 in rice immunity

Monday, July 14, 2025
13:30 - 15:15  
Location: Confex Hall 3
Extracellular & Intracellular non-self recognition & signaling

The rice U-box ubiquitin ligase PUB44, targeted by the Xanthomonas oryzae effector XopP, functions as a positive regulator of pattern-triggered immunity (Ishikawa et al. Nat Commun 2014). Upon PAMP perception, PUB44 interacts with and ubiquitinates PBI1, a negative regulator of WRKY45, a key transcription factor in rice immunity. PUB44-mediated degradation of PBI1 leads to the activation of WRKY45-dependent immune responses (Ichimaru et al. Nat Commun 2022). We found that PUB44 undergoes phosphorylation following PAMP perception. We identified six phosphorylation sites of PUB44. Most of the sites are phosphorylated by MAP kinases, suggesting that the PUB44 enzymatic activation may be regulated through MAP kinase-mediated phosphorylation. Alanine substitution mutants of these phosphorylation sites revealed a critical residue required for the multisite phosphorylation of PUB44. Recent study has reported that the predicted protein structures of the C-terminal domains conserved in the Xanthomonas XopP family resemble those of mammal mTOR kinases. A transient assay using rice protoplasts indicates that the C-terminal domain of XopP plays a crucial role in inhibiting PUB44 function. In this presentation, we will discuss how PUB44 is activated via MAP kinase-mediated multisite phosphorylation and how the XopP effector suppresses PUB44 activity.