Comparative functional analysis of the velvet gene family reveals unique roles in fungal development and pathogenicity in Magnaporthe oryzae.

The ascomycete fungus Magnaporthe oryzae is an economically important pathogen that causes rice blast disease worldwide. Accumulating evidence indicates that the fungal velvet genes are key regulators of a number of cellular processes, including development, pathogenicity and secondary metabolism, in many species of fungi. In this study, we identified and functionally characterized four genes (MoVOSA, MoVELB, MoVEA, and MoVELC) from the genome of the fungal pathogen M. oryzae. These genes were homologous to the velvet gene family of Aspergillus nidulans. Deletions of MoVEA, MoVELB, and MoVELC resulted in a significant decrease in conidiation, indicating their roles as positive regulators thereof. The MoVELC gene was involved in development of conidial morphology, while MoVELB and MoVEA appeared necessary for conidial germination, MoVEA further being indispensable for appressorial development and modulation of reactive oxygen species in disease development. Deletion of MoVELC affected the cell wall integrity of appressoria, resulting in failure to penetrate host cells. Unexpectedly, MoVOSA appeared dispensable for the development and pathogenicity of M. oryzae, even though its homologs play specific roles in other fungal species. Taken together, our data demonstrate that the velvet genes are linked to M. oryzae infection-related development and pathogenicity, and the findings provide a framework for comparative studies of the conserved velvet gene family across a range of fungal taxa, which may provide new insight into fungal development and pathogenicity.