Ustilago Maydis Mating

Fungal Genetics and Biology 20, 299–312 (1996) Article No. 0044

Ustilago maydis Mating Hyphae Orient Their Growth toward Pheromone Sources

Karen M. Snetselaar,*,1 Michael Bolker,† and RegineKahmann† ¨
*Department of Biology, St. Joseph’s University, 5600 City Avenue, Philadelphia, Pennsylvania 19131; ¨ ¨ ¨ and †Institut fur Genetik und Mikrobiologie, Universitat Munchen, Maria-Ward-Str.1a, 80638 Munich, Germany

Accepted for publication October 18, 1996

Snetselaar, K. M., Bolker, M., and Kahmann, R. 1996. ¨ Ustilago maydis mating hyphae orient their growth toward pheromonesources. Fungal Genetics and Biology 20, 299–312. When small drops of Ustilago maydis sporidia were placed 100–200 mm apart on agar surfaces and covered with paraffin oil, sporidia from one drop formedthin hyphae that grew in a zig-zag fashion toward the other drop if it contained sporidia making the appropriate pheromone. For example, a2b2 mating hyphae grew toward a1b1 and a1b2 mating hyphae, andthe filaments eventually fused tip to tip. Time-lapse photography indicated that the mating hyphae can rapidly change orientation in response to nearby compatible sporidia. When exposed to pheromoneproduced by cells in an adjacent drop, haploid sporidia with the a2 allele began elongating before sporidia with the a1 allele. Sporidia without functional pheromone genes responded to pheromone althoughthey did not induce a response, and sporidia without pheromone receptors induced formation of mating hyphae although they did not form mating hyphae. Diploid sporidia heterozygous at b but not at aformed straight, rigid, aerial filaments when exposed to pheromone produced by the appropriate haploid sporidia. Again, the a2a2b1b2 strain formed filaments more quickly than the a1a1b1b2 strain. Takentogether, these results suggest that the a2 pheromone diffuses less readily or is degraded more quickly than the a1 pheromone. r 1996 Academic Press

Index Descriptors: Ustilago; pheromone;...