Light regulates a Phycomyces blakesleeanus gene family similar to the carotenogenic repressor gene of Mucor circinelloides.

The transcription of about 5-10 % of the genes in Phycomyces blakesleeanus is regulated by light. Among the most up-regulated, we have identified four genes, crgA-D, with similarity to crgA of Mucor circinelloides, a gene encoding a repressor of light-inducible carotenogenesis. The four proteins have the same structure with two RING RING Finger domains and a LON domain, suggesting that they could act as ubiquitin ligases, as their M. circinelloides homolog. The expression of these genes is induced by light with different thresholds as in other Mucoromycotina fungi like Blakeslea trispora and M. circinelloides. Only the P. blakesleeanus crgD gene could restore the wild type phenotype in a M. circinelloides null crgA mutant suggesting that P. blakesleeanus crgD is the functional homolog of crgA in M. circinelloides. Despite their sequence similarity it is possible that the P. blakesleeanus Crg proteins do not participate in the regulation of beta-carotene biosynthesis since none of the carotene-overproducing mutants of P. blakesleeanus had mutations in any of the crg genes. Our results provide further support of the differences in the regulation of the biosynthesis of beta-carotene in these two Mucoromycotina fungi.