Roles of Forkhead-box Transcription Factors in Controlling Development, Pathogenicity, and Stress Response in Magnaporthe oryzae

Although multiple transcription factors (TFs) have been characterized via mutagenesis to understand their roles in controlling pathogenicity and infection-related development in Magnaporthe oryzae, the causal agent of rice blast, if and how forkhead-box (FOX) TFs contribute to these processes remain to be characterized. Four putative FOX TF genes were identified in the genome of M. oryzae, and phylogenetic analysis suggested that two of them (MoFKII1 and MoHCM1) correspond to Ascomycota-specific members of the FOX TF family while the others (MoF0X1 and MoF0X2) are Pezizomycotina-specific members. Deletion of MoFKH1 (Delta MofIchl) resulted in reduced mycelial growth and conidial germination, abnormal septation and stress response, and reduced virulence. Similarly, Delta Mohcm1 exhibited reduced mycelial growth and conidial germination. Conidia of Delta Mofkh1 and Delta Mohcm1 were more sensitive to one or both of the cell cycle inhibitors hydroxyurea and benomyl, suggesting their role in cell cycle control. On the other hand, loss of MoFOX1 (Delta Mofoxl) did not show any noticeable changes in development, pathogenicity, and stress response. Deletion of MoF0X2 was not successful even after repeated attempts. Taken together, these results suggested that MoFKH1 and MoHCM1 are important in fungal development and that MoFKH1 is further implicated in pathogenicity and stress response in M. oryzae.