REGULATORY GENES-CONTROLLING MPG1 EXPRESSION AND PATHOGENICITY IN THERICE BLAST FUNGUS MAGNAPORTHE-GRISEA

MPG1, a pathogenicity gene of the rice blast fungus Magnaporthe grisea , is expressed during pathogenesis and in axenic culture during nitrog en or glucose limitation. We initiated a search for regulatory mutatio ns that would impair nitrogen metabolism, MPG1 gene expression, and pa thogenicity. First, we developed a pair of laboratory strains that wer e highly fertile and pathogenic toward barley. Using a combinatorial g enetic screen, we identified mutants that failed to utilize a wide ran ge of nitrogen sources (e.g., nitrate or amino acids) and then tested the effect of these mutations on pathogenicity. We identified five mut ants and designated them Nr(-) (for nitrogen regulation defective). We show that two of these mutations define two genes, designated NPR1 an d NPR2 (for nitrogen pathogenicity regulation), that are essential for pathogenicity and the utilization of many nitrogen sources. These gen es are nonallelic to the major nitrogen regulatory gene in M. grisea a nd are required for expression of the pathogenicity gene MPG1. We prop ose that NPR1 and NPR2 are major regulators of pathogenicity in M. gri sea and may be novel regulators of nitrogen metabolism in fungi.