A gene related to yeast HOS2 histone deacetylase affects extracellular depolymerase expression and virulence in a plant pathogenic fungus

A gene, HDC1, related to the Saccharomyces cerevisiae histone deacetylase ( HDAC) gene HOS2, was isolated from the filamentous fungus Cochliobolus carb onum, a pathogen of maize that makes the HDAC inhibitor HC-toxin. Engineere d mutants of HDC1 had smaller and less septate conidia and exhibited an sim ilar to 50% reduction in total HDAC activity. Mutants were strongly reduced in virulence as a result of reduced penetration efficiency. Growth of hdc1 mutants in vitro was normal on glucose, slightly decreased on sucrose, and reduced by 30 to 73% on other simple and complex carbohydrates. Extracellu lar depolymerase activities and expression of the corresponding genes were downregulated in hdc1 mutant strains. Except for altered conidial morpholog y, the phenotypes of hdc1 mutants were similar to those of C. carbonum stra ins mutated in ccSNF1 encoding a protein kinase necessary for expression of glucose-repressed genes. These results show that HDC1 has multiple functio ns in a filamentous fungus and is required for full virulence of C. carbonu m on maize.