COP9 Signalosome’s Role in Plant Defense Mechanisms

The COP9 signalosome (CSN) is a highly conserved eukaryotic protein complex that plays a crucial role in plant growth, development, and stress responses by modulating the ubiquitination pathway. Emerging evidence underscores its significance in plant immunity, where it orchestrates diverse defense mechanisms, including hormone signaling, reactive oxygen species (ROS), homeostasis, and secondary metabolite (SM) biosynthesis. As a key regulator, CSN influences multiple layers of immune responses, such as pattern-triggered immunity (PTI), effector-triggered immunity (ETI), and systemic acquired resistance (SAR). However, the intricate interplay between CSN and immune regulatory networks remains incompletely understood, and a comprehensive model of its mechanistic framework is still lacking. This review systematically consolidates current knowledge on CSN-mediated immune regulation in plant–pathogen interactions and highlights its role in disease resistance.