Rice blast is a devastating plant disease caused by the fungus Magnaporthe grisa. Genetic analysis with this fungal pathogen has demonstrated that numerous genetic loci are required for infecting and destroying rice plants. Because of the genetic and biochemical tractability of this fungus and its cultivated host plant, we have decided that this disease represents a unique opportunity to begin a detailed genetic and molecular analysis of fungal pathogenicity on rice by altering the shape of various fungal cells necessary for rice plant infection. We have named this genetic locus, SMO because Smo-mutations dramatically alter the shape of the asexual spores (spore morphology). In this proposal, we described our approach to cloning and analyzing the function of the SMO locus. We shall clone the SMO locus by complementation of Smo-mutants with cloned M.grisea DNA. We will prove by genetic analysis, that DNA fragments that complement the Smo-phenotype encode the SMO gene. We will sequence the wild type SMO gene and begin an analysis of the function of the SMO gene product. We will also use cloned DNA fragments to investigate the origin of Smo-mutations, which appear to occur at a high frequency. Finally we will investigate the consequences of Smo-mutations on M.grisea growth inside rice plants. The results of this research will provide new information on the formation of infection structures in plant pathogenic fungi, as well as provide insights into the mechanisms of cell shape determination in fungi.
