The multifunctional role of the COP9 signalosome in eukaryotic development, immunity, and environmental adaptation

We integrate recent mechanistic advances to define CSN as a central regulatory hub coordinating deneddylation, signaling, transcription, and stress responses across plant developmental and immune pathways. The CSN (COP9 signalosome) is an evolutionarily conserved multiprotein complex initially identified in Arabidopsis thaliana as a negative regulator of photomorphogenesis. Subsequent studies across diverse organisms have revealed that CSN plays central roles in a wide array of biological processes, including protein degradation, hormone signaling, stress adaptation, development, and immunity. The CSN exerts its core function through deneddylation of cullin-RING E3 ubiquitin ligases, thereby regulating protein turnover via the ubiquitin-proteasome system. In plants, CSN integrates external signals such as light and pathogens to fine-tune developmental programs and defense responses. Recent research highlights its regulatory functions in secondary metabolism, flowering time, reactive oxygen species homeostasis, and stress-induced epigenetic memory. Additionally, pathogens have evolved effectors to hijack CSN-mediated processes to suppress host immunity. This review focuses specifically on the multifunctional roles and regulatory mechanisms of CSN in plants, highlighting novel insights into its emerging roles in transcriptional and epigenetic regulation. Unlike previous summaries, we integrate recent mechanistic advances and cross-kingdom perspectives to provide a comprehensive framework for understanding CSN as a central node in the dynamic regulation of eukaryotic cellular functions.