GENETIC ORGANIZATION OF A REPEATED DNA-SEQUENCE FAMILY IN THE RICE BLAST FUNGUS

The fungal rice pathogen Magnaporthe grisea contains repetitive DNA sequences called MGR. We have used a DNA probe, MGR586, derived from these sequences and crosses between rice-pathogenic and non-rice-pathogenic laboratory strains of M. grisea to rapidly map genes in this organism. The rice-pathogenic strain contained 57 EcoRI restriction fragments that hybridize to the MGR586 probe; the other rive non-rice-pathogenic parent strains contained a single MGR586 sequence. Genetic analysis of MGR segregation detected eight linkage groups and allowed the mapping of three pigmentation genes (Alb1, Rsy1, and Buf1), the mating type locus (Matl), the nucleolar organizer (Rdn1), the Smo1 gene, and two restriction fragment length polymorphisms linked to Smo1. Our results indicate that the MGR586 loci are randomly distributed about the M. grisea genome and permit the construction of a well-marked linkage map useful for future studies on genome organization and genetic analysis in M. grisea.