Recent studies on pathogenicity genes in rice blast fungus, Magnaporthe grisea

摘要

Rice blast is the most damaging disease in rice growing areas throughout the world. The causal agent of rice blast disease is an ascomycete fungus Magnaporthe grisea. M. grisea is highly suited for research on fungal pathogenicity, since many experimental tools including classical and molecular genetic technique are available. Several genes affecting pathogenicity have been isolated from M. grisea which can be called 'pathogenicity genes' in the broad sense (see Schafer, 1994). Those genes are divided into three groups: genes for plant-specific nutrition, genes for infection-related morphogenesis and genes for symptom development and disease establishment. The first group of genes provide important information for understanding the physiology of invasive fungal growth. Insertional mutagenesis have identified that PTH3 encoding a histidine biosynthesis enzyme is. necessary for full pathogenicity (Sweigard et al., 1998) and that a mutant exhibiting methionine auxotrophy shows reduced pathogenicity (Balhadere et al., 1999). The second group is currently represented by genes encoding signal transduction components involved in infection-related morphogenesis. Recently, we identified the first example of a gene which may be classified into the third group (Urban et al., 1999). Here, we focus on the second and third groups of pathogenicity genes.