Milenovic, M.; Jozwiak, A.; Judelson, H. S.

Sexual reproduction by heterothallic species of Phytophthora involves communication between its two mating types by diterpenoid hormones derived from plant phytol. The genetics of mating type determination have remained unknown. We identified a conserved gene cluster that links mating identity to 2 hormone biosynthesis. Functional perturbation in P. infestans and pathway reconstruction in yeast showed that a cytochrome P450 in the cluster performs a mating type-specific step in hormone production. Comparative analyses revealed that the hormonal system is implemented through distinct genetic mechanisms in different species, including mating type-specific transcription in P. infestans and hemizygous inheritance in P. capsici. In self-fertile species the cluster is often eroded. These findings reveal a genetic basis for mating type and how conserved signaling systems can be evolutionarily remodeled.