A gene for carotene cleavage required for pheromone biosynthesis and carotene regulation in the fungus Phycomyces blakesleeanus

Mating and sexual development in fungi are controlled by molecular mechanisms that are specific for each fungal group. Mating in Phycomyces blakesleeanus and other Mucorales requires pheromones derived from β-carotene. Phycomyces mutants in gene carS accumulate large amounts of β-carotene but do not enter the sexual process. We show that carS encodes a β-carotene-cleaving oxygenase that catalyzes the first step in the biosynthesis of a variety of apocarotenoids, including those that act as pheromones. Therefore carS mutants cannot stimulate their sexual partners, although they respond to them. CarS catalyzes the biosynthesis of a β-ring-containing apocarotenoid that inhibits the activity of the carotenogenic enzyme complex in vegetative cells and provides a feedback regulation for the β-carotene pathway. The carS gene product is a keystone in carotenogenesis and in sexual reproduction.