GENETIC AND PHYSICAL MAPPING OF TELOMERES IN THE RICE BLAST FUNGUS, MAGNAPORTHE-GRISEA

Telomeric restriction fragments were genetically mapped to a previousl y described linkage map of Magnaporthe grisea, using RFLPs identified by a synthetic probe, (TTAGGG)(3). Frequent rearrangement of telomeric sequences was observed in progeny isolates creating a potential for m isinterpretation of data. Therefore a consensus segregation data set w as used to minimize mapping errors. Twelve of the 14 telomeres were fo und to be genetically linked to existing RFLP markers. Second-dimensio nal electrophoresis of restricted chromosomes confirmed these linkage assignments and revealed the chromosomal location of the two unlinked telomeres. We were thus able to assign all 14 M. grisea telomeres to t heir respective chromosome ends. The Achilles' cleavage (AC) technique was employed to determine that chromosome 1 markers II and CH5-120H w ere similar to 1.8 Mb and 1.28 Mb, respectively, from their nearest te lomeres. RecA-AC was also used to determine that unlinked telomere 6 w as similar to 530 kb from marker CH5-176H in strain 2539 and 580 kb in Guy11. These experiments indicated that large portions of some chromo some ends are unrepresented by genetic markers and provided estimates of the relationship of genetic to physical distance in these regions o f the genome.