cigA, a light-inducible gene involved in vegetative growth in Mucor circinelloides is regulated by the carotenogenic repressor crgA.

A strategy based on the differential-display technique has been applied to identify and to isolate potential target genes controlled by crgA, a negative regulator of the light-inducible carotenogenesis in the fungus Mucor circinelloides. This approach resulted in the identification and cloning of the gene cigA, whose expression is repressed by the crgA gene. After a light pulse, there is an immediate though transient accumulation of transcripts of cigA gene. A similar result was obtained when mycelia were exposed to continuous illumination, suggesting the existence of a photoadaptation mechanism in M. circinelloides. The protein sequence deduced from the nucleotide sequence of cigA shows homology to the mouse and human GDP-fucose protein O-fucosyltransferases. Null cigA mutants were generated by gene replacement. Lack of cigA function does not affect carotenogenesis but provokes a slight reduction in vegetative growth that is independent of light. Introduction of wild-type cigA alleles into a cigA- strain restored the wild-type phenotype for vegetative growth. These results suggest that cigA is involved in vegetative growth and, moreover, that crgA controls cellular processes other than carotenogenesis.