Random mutagenesis screen shows that Phytophthora capsici CRN83_152 mediated cell death is not required for its virulence function(s)

With the increasing availability of plant pathogen genomes, secreted proteins that aid infection (effectors) have emerged as key factors that help govern plant-microbe interactions. The conserved CRN (CRinkling and Necrosis) effector family was first described in oomycetes by their capacity to induce host cell death. Despite recent advances towards elucidation of CRN virulence functions, the relevance of CRN induced cell death remains unclear. In planta over-expression of PcCRN83_152, a CRN effector from P. capsici, causes host cell death and boosts P. capsici virulence. We used these features to ask whether PcCRN83_152 induced cell death is linked to its virulence function. By randomly mutating this effector, we generated PcCRN83_152 variants with no cell death phenotypes (NCD), which were subsequently tested for activity towards enhanced virulence. We show that a subset of PcCRN83_152 NCD variants retain their ability to boost P. capsici virulence. Moreover, NCD variants were shown to have a suppressive effect on PcCRN83_152 mediated cell death. Our work shows that PcCRN83_152 induced cell death and virulence function can be separated. Moreover, if these findings hold true for other cell death-inducing CRN effectors, this work in turn, will provide a framework for studies aimed at unveiling the virulence functions of these effectors.