Ubiquitination of OsCSN5 by OsPUB45 activates immunity by modulating the OsCUL3a-OsNPR1 module.

Abstract

The COP9 signalosome (CSN) is a highly conserved protein complex in eukaryotes, with CSN5 serving as its critical catalytic subunit. However, the role of CSN5 in plant immunity is largely unexplored. Here, we found that suppression of <i>OsCSN5</i> in rice enhances resistance against the fungal pathogen <i>Magnaporthe oryzae</i> and the bacterial pathogen <i>Xanthomonas oryzae</i> pv. <i>oryzae</i> (<i>Xoo</i>) without affecting growth. OsCSN5 is ubiquitinated and degraded by the E3 ligase OsPUB45. Overexpression of <i>OsPUB45</i> increased resistance against <i>M. oryzae</i> and <i>Xoo</i>, while dysfunction of <i>OsPUB45</i> decreased resistance. In addition, OsCSN5 stabilized OsCUL3a to promote the degradation of a positive regulator OsNPR1. Overexpression of <i>OsPUB45</i> compromised accumulation of OsCUL3a, leading to stabilization of OsNPR1, whereas mutations in <i>OsPUB45</i> destabilized OsNPR1. These findings suggest that OsCSN5 stabilizes OsCUL3a to facilitate the degradation of OsNPR1, preventing its constitutive activation without infection. Conversely, OsPUB45 promotes the degradation of OsCSN5, contributing to immunity activation upon pathogen infection.