CALCIUM-DEPENDENT PROTEOLYSIS OF THE ARABIDOPSIS DAMP PRECURSOR PROPEP1 BY THE CYSTEINE PROTEASE METACASPASE4 REVEALS A CONSERVED MECHANISM FOR IMMEDIATE RELEASE OF PEPTIDE SIGNALS DURING WOUND RESPONSES

In animals, one of the most immediate responses to tissue wounding comprises the release of peptide signals such as interleukins from their precursor proteins. Although the wound response has been intensively studied in plants as well, little is known about plant peptides with cytokine-like functions. Here we report that in Arabidopsis thaliana, wounding triggers the instantaneous activation of the METACASPASE4 cysteine protease and subsequent cleavage of the PROPEP1 precursor to release the mature peptide signal PEP1, which induces basal immunity against pathogens. Furthermore, confocal microscopy of targeted cell damage by laser wounding revealed that the inactive zymogen of MC4 and PROPEP1 reside in the cytosol until a constitutive increase in calcium concentration upon cell membrane integrity loss triggers MC4 activation and PROPEP1 cleavage. PROPEP1 cleavage and PEP1 release is restricted to only a few cells surrounding the damaged site. Our results highlight the similarities of the spatiotemporal dynamics and control mechanisms of the plant wound response as an example for convergent evolution with respect to the mammalian system, in which calpain releases IL1-α from its precursor.