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 marke rs to previously generated maps. The new map consists of 203 markers r epresenting 132 independently segregating: loci and spans approximatel y 900 cM with an average resolution of 4.5 cM. Mapping of 33 cosmid pr obes from the genetic map generated by Sweigard et ill, has allowed th e integration of two M. grisea maps. The integrated map showed that th e linear order of markers along all seven chromosomes in both maps is in good agreement. Thirty of eighty seven markers were derived from co smid clones that contained the retrotransposon MAGGY (M. grisea gypsy element). Mapping of single-copy DNA sequences associated with the MAG GY cosmids indicated that MAGGY elements are scattered throughout the fungal genome. In eight cases? the probes associated with MAGGY elemen ts 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, identif ied sequences that were duplicated in the Guy11 genome. Most of the MA GGY cosmids also contained other classes of repetitive DNA suggesting that repetitive DNA sequences tend to cluster in the M. grisea genome.