Figure 2.

Secreted Proteases and Protease Inhibitors in Plant–Microbe Interactions.

In response to pathogen infection, plants secrete different types of proteases into the apoplastic region. Plant-derived proteases contribute to plant immune response via different mechanisms. The Arabidopsis secreted protein SAP1/2 suppresses bacterial growth by directly cleaving bacterial growth-related protein MucD. Other proteases, such as P69B/C, RCR3, and PLCPs, also recognize and cleave their substrates in the apoplast. The released peptides can be recognized by host membrane-localized receptor-like kinases, leading to the activation of immune responses. To counter host protease-mediated immunity, pathogens can secrete protease inhibitors to suppress host protease activity via direct interactions or secrete effectors, such as PsAvh240 and Avrblb2, which block the secretion of plant proteases.