A fungal GPI-anchored protein gene functions as a virulence and antiviral factor

We show that a gene (CpGap1) encoding a glycosylphosphatidylinositol-anchored protein (GPI-AP) of the chestnut blight fungus Cryphonectria parasitica is differentially expressed by Cryphonectria hypovirus 1 (CHV1) infection. Functional analysis using a CpGap1-null mutant results in no observed changes in cultural morphology other than hypersensitivity to ROS. Analysis of the protein product of the CpGap1 gene (CpGAP1) confirmed motifs with antioxidizing properties. The virulence of the CpGap1-null mutant is significantly decreased, and phytotoxic activity is seen in the peptides of CpGAP1. CHV1 transfer to the CpGap1-null mutant results in severely retarded colonial growth, and virus-titer is significantly increased in the mycelia of CHV1-infected CpGap1-null mutant. These results indicate that CpGAP1 functions as a protective barrier against plant defenses, but also acts as a virulence factor. Moreover, our study demonstrates that the CpGap1 gene is a host-tolerating antiviral factor that helps maintain fungal growth and suppress viral titer after CHV1 infection.