Regulatory plasticity of the 26S proteasome in plants

The plant 26S proteasome is itself a regulatory target. Its abundance, composition, activity, and subcellular localisation are dynamically modulated by the very signalling pathways whose components or regulatory proteins it degrades. In this review, we draw on recent advances across immunity, abiotic stress, hormone signalling, organelle communication, and the proteasome's interplay with autophagy, together with the non-proteolytic functions of the 19S regulatory particle and apoplastic proteasomes, to establish the proteasome as a hub of regulatory plasticity. We argue that the proteasome operates not as a static degradation machine but as a proteolytic resource whose allocation across assembly states, subcellular compartments, and degradation pathways is continuously reconfigured. The central regulatory decision is therefore not which substrate is degraded, but how proteolytic capacity itself is distributed. This regulatory plasticity, and the nodes that mediate it, may inform the development of strategies to enhance proteolytic capacity for crop resilience.