This research concerns the morphological and biochemical specialization demonstrated by the rice blast fungus, Magnaporthe grisea. Asexual spores of M. grisea attach to plant surfaces, initiate growth through the emergence of a germ tube, and differentiate an infection structure called an appressorium (1). The appressorium is a specialized cell capable of generating enormous turgor pressures that facilitate the direct penetration of the plant epidermis (2). Large, swollen, infectious hyphae rapidly appear within and between plant cells (3). Finally, surface borne conidiophores produce numerous asexual spores to reinitiate the disease cycle. The goal of this research is to understand the biochemical events that key disease-related morphogenesis in M. grisea. Genetic and biochemical investigations can identify components in this process that could elucidate central processes in fungal cell morphogenesis and may provide strategies for the development of novel disease control measures. Previous investigations identified a genetic locus termed SMO1 (4). Phenotypic analysis suggests that the SMO gene product plays a central role in establishing the polarity of cell growth and morphogenesis in particular disease-related cell types of M. grisea and thus Smo-mutations reduce pathogenicity towards rice. Additionally, mutations at this locus occur at a high frequency in certain genetic backgrounds of M. grisea. The SMO locus has been cloned by a novel mapped based cloning procedure developed by this laboratory for M. grisea. The studied have demonstrated that SMO is closely linked to chromosomal duplication. To advance the understanding of the SMO locus and its relationship to fungal growth and disease-related morphogenesis, three related experimental strategies will be used: (1) A fine structure analysis of the SMO locus and smo-minus. (2) Cytological and biochemical identification of the SMO protein and more refined characterization of the duplication around the SMO locus. (3) The isolation and characterization of additional mutations affecting disease-related morphogenesis in M. grisea. %%% The fungus Magnaporthe grisea is an economically significant pathogen of rice. The goal of this research is to increase our understanding of the process by which this fungus undergoes the structural changes necessary to initiate an infection. The investigator will be studying a gene which he has already shown to function in the development by the fungus of a specialized infection structure and will identify and characterize other mutations affecting morphogenesis related to the infection process.
