MATING-TYPE GENES FROM THE HOMOTHALLIC FUNGUS SORDARIA-MACROSPORA AREFUNCTIONALLY EXPRESSED IN A HETEROTHALLIC ASCOMYCETE

Homokaryons from the homothallic ascomycte Sordaria macrospora are abl e to enter the sexual pathway and to form fertile fruiting bodies. To analyze the molecular basis of homothallism and to elucidate the role of mating-products during fruiting body development, ive cloned and se quenced the entire S. macrospora mating-type locus. Comparison of the Sordaria mating-type locus with mating-type idiomorphs from the hetero thallic ascomycetes Neurospora crassa and Podospora anserina revealed that sequences from both idiomorphs (A/a and mat-/mat+, respectively) are contiguous in S. macrospora. DNA sequencing of the S. macrospora m ating-type region allowed the identification of four open reading fram es (ORFs), which were termed Smt-a1, SmtA-1, SmtA-2 and SmtA-3. While Smt-a1, SmtA-1, and SmtA-2 show strong sequence similarities with the corresponding N. crassa mating-type ORFs, SmtA-3 has a chimeric charac ter. It comprises sequences that are similar to the A and a mating-typ e idiomorph from N. crassa. To determine functionality of the S. macro spora mating-type genes, we show that all ORFs are transcriptionally e xpressed. Furthermore, we transformed the S. macrospora mating-type ge nes into mat- and mat+ strains of the closely related heterothallic fu ngus P. anserina. The transformation experiments show that mating-type genes from S. macrospora induce fruiting body formation in P. anserin a.