Extracellular proteases from microbial plant pathogens as virulence factors

Plant pathogens deploy specialized proteins to aid disease progression, some of these proteins function in the apoplast and constitute proteases. Extracellular virulence proteases have been described to play roles in plant cell wall manipulation and immune evasion. In this review, we discuss the evidence for the hypothesized virulence functions of bacterial, fungal, and oomycete extracellular proteases. We highlight the contrast between the low number of elucidated functions for these proteins and the size of extracellular protease repertoires among pathogens. Finally, we suggest that the refinement of in planta ‘omics’ approaches, combined with recent advances in modeling and mechanism-based methods for trapping substrates finally make it possible to address this knowledge gap.