Genome organization of Magnaporthe grisea: genetic map, electrophoretic karyotype, and occurrence of repeated DNAs

Abstract

A genetic map of Magnaporthe grisea (anamorph=Pyricularia oryzae and P. grisea), the causal agent of rice blast disease, was generated from segregation data utilizing 97 RFLP markers, two isoenzyme loci and the mating type locus among progeny of a cross between parental strains Guy 11 and 2539. Of the seven chromosomes of M. Grisea, three were resolved by contour-clamped homogeneous electric field (CHEF) electrophoresis, while the remaining four migrated as two doublet bands. By utilizing differences between CHEF mobilities of unresolved chromosomes from the parental strains, Southern analysis with selected markers allowed the chromosomal assignment of all linkage groups. A small translocation involving 1 marker was found in the parental strains used to produce the segregating population from which the map was constructed. Nine classes of repetitive DNA elements were found in the genome of a fungal isolate pathogenic to rice. These occurred only a few times or not at all in the genomes of isolates showing reduced virulence on rice. One repetitive DNA was shown to have structural similarity to the Alu sequences found in primates, a sequence similarity to the copia-like elements of Drosophila, and peptide similarity to transposable elements found in Drosophila, other fungi, and higher plants.