Abstract

Homeostatic regulation of proteolytic activity is fundamental to plant cellular physiology, and dysregulated protease-like activities are frequently associated with cytotoxic or stress-induced cell death. Here, we identify RipBH, a previously uncharacterized type III-secreted protein from Ralstonia solanacearum , as an intracellular self-cleaving protease-like effector with the capacity to perturb host physiological balance. RipBH harbors a papain-like catalytic core and multiple ankyrin repeats; structural mutagenesis showed that conserved catalytic residues (C135, H244, D268, and N117) are indispensable for self-processing and cell death–inducing activity. RipBH undergoes auto-cleavage inside plant cells, producing smaller fragments that are detectable in both the cytoplasm and nucleus. Truncation of ankyrin repeats altered cleavage behavior and abolished cell-death induction, supporting the idea that ankyrin-mediated structural constraints function as a regulatory module required for activation. Importantly, RipBH-induced necrosis occurred largely independently of the tested canonical ETI-related signaling components, suggesting a physiology-centered disruption pathway rather than immune receptor-mediated recognition. We propose that RipBH operates as a pathogen-encoded proteolytic switch that destabilizes intracellular homeostasis, providing a potential mechanistic link between effector auto-processing and necrosis-like physiological collapse under biotic stress. Our findings contribute to the conceptual framework of proteolysis-associated plant cell dysfunction and highlight pathogen-driven interference with core physiological processes.