Evolution and organization of a highly dynamic, subtelomeric helicase gene family in the rice blast fungus Magnaporthe grisea.

Sequence analysis of a 13-kb telomeric region in O-137, a rice pathogenic isolate of Magnaporthe grisea, uncovered a novel gene, designated TLH1 (telomere-linked helicase 1). The TLH1 gene is a member of a gene family, and the sequences flanking this gene family have also been amplified. Genetic mapping showed that most members of the TLH gene family are tightly linked to the telomeres. A physical mapping technique, termed RecA-mediated Achilles' heel cleavage, and cloning and sequencing of two additional telomeres of O-137 associated with the TLH gene family confirmed that most members of the TLH gene family are located within 10 kb from the telomeric repeat. A survey of M. grisea strains from diverse hosts revealed that the gene family is ubiquitously present among rice pathogens, but is absent from almost all isolates of hosts other than rice. The gene family appears to be highly dynamic, undergoing frequent deletion/amplification events. Given the presence of similar helicase gene families in chromosome ends of Saccharomyces cerevisiae and Ustilago maydis, the initial association of helicase genes with fungal telomeres might date back to very early stages of the fungal evolution.