Genome organization of Magnaporthe grisea: Integration of genetic maps, clustering of transposable elements and identification of genome duplications and rearrangements

A high-density genetic map of the rice blast fungus Magnaporthe grisea (Guy11 x 2539) was constructed by adding 87 cosmid-derived RFLP markers to previously generated maps. The new map consists of 203 markers representing 132 independently segregating: loci and spans approximately 900 cM with an average resolution of 4.5 cM. Mapping of 33 cosmid probes from the genetic map generated by Sweigard et ill, has allowed the integration of two M. grisea maps. The integrated map showed that the linear order of markers along all seven chromosomes in both maps is in good agreement. Thirty of eighty seven markers were derived from cosmid clones that contained the retrotransposon MAGGY (M. grisea gypsy element). Mapping of single-copy DNA sequences associated with the MAGGY cosmids indicated that MAGGY elements are scattered throughout the fungal genome. In eight cases? the probes associated with MAGGY elements showed abnormal segregation patterns. This suggests that MAGGY may be involved in genomic rearrangements. Two RFLP probes linked to MAGGY elements, and another flanking other repetitive DNA elements, identified sequences that were duplicated in the Guy11 genome. Most of the MAGGY cosmids also contained other classes of repetitive DNA suggesting that repetitive DNA sequences tend to cluster in the M. grisea genome.