Mating-Type Genes Control Sexual Reproduction, Conidial Germination, and Virulence in Cochliobolus lunatus

Cochliobolus lunatus (anamorph: Curvularia lunata) is a major pathogenic fungus that causes the Curvularia leaf spot of maize. ClMAT1-1-1 and ClMAT1-2-1, the C. lunatus orthologs of C. heterostrophus ChMAT1-1-1 and ChMAT1-2-1, were investigated in the present study to uncover their functions in C. lunatus. Southern blot analysis showed that these mating-type MAT genes exist in the C. lunatus genome as a single copy. ClMAT1-1-1 and ClMAT1-2-1 were knocked out and complemented to generate Delta Clmat1-1-1 and Delta Clmat1-2-1 and Delta Clmat1-1-1-C and Delta Clmat1-2-1-C, respectively. The mutant strains had defective sexual development and failed to produce pseudothecia. There were no significant differences in growth rate or conidia production between the mutant and wild-type strains. However, the aerial mycelia and mycelial dry weight of Delta Clmat1-1-1 and Delta Clmat1-2-1 were lower than those of wild type, suggesting that MAT genes affect asexual development. ClMAT genes were involved in the responses to cell wall integrity and osmotic adaptation. Delta Clmat1-2-1 had a lower conidial germination rate than the wild-type strain CX-3. The virulence of Delta Clmat1-2-1 and Delta Clmat1-1-1 was also reduced compared with the wild-type. Complementary strains could restore all the phenotypes.