XCP1 cleaves Pathogenesis-related protein 1 into CAPE9 for systemic immunity in Arabidopsis

The significant breakthrough of this research is the successful determination of the physiological function and activity of PR1, confirming PR1 as the precursor protein of a highly active immune cytokine CAPE. In response to bacterial infections, plants must utilize a specific protease conducting caspase-like activity to release CAPE from PR1 to initiate systemic defense responses. We proposed the functional name of this enzyme as Enzyme Specific for CAPE Production (ESCAPE). This study further identifies XCP1 as the protein possessing ESCAPE function, with its enzymatic activity for CAPE production being highly temperature-sensitive. Importantly, plants lacking XCP1 cannot effectively activate systemic defense responses upon sensing a conserved molecular pattern from bacteria. Moreover, even when plants cannot synthesize or perceive salicylic acid, direct application of trace amounts of CAPE can still activate systemic defense responses in plants. As salicylic acid serves as a central signaling role for plants to counteract pathogen attacks, many pathogens inhibit its mechanism in various ways to enhance their virulence. Recent reports also indicate that a warming climate directly affects the broad-spectrum defense response mediated by salicylic acid. Combining these findings with the present study, this phenomenon might be related to the thermo-sensitive activity of plant ESCAPE (XCP1). Therefore, the direct application of CAPE peptides or the optimization of mechanisms for CAPE production within plants could contribute to broadly enhancing defense capabilities against diseases. This research outcome holds vital implications for bolstering crop disease resistance and offers a new perspective for addressing the impact of global warming on plant immunity.

Co-researchers:Ying-Lan Chen, Fan-Wei Lin, Kai-Tan Cheng, Chi-Hsin Chang, Sheng-Chi Hung, Thomas Efferth