Blue light signaling chains in Phycomyces: phototransduction of carotenogenesis and morphogenesis involves distinct protein kinase/phosphatase elements.

Carotenogenesis and morphogenesis represent two of the several responses sensitive to blue light which characterize the lower eukaryote Phycomyces blakesleeanus. Speculating that reversible phosphorylation may be an intracellular event beyond the photoperception step, we resorted to the use of first-choice inhibitors of protein phosphatases and protein kinases. The mycelial beta-carotene content of dark-grown cultures was induced by all agents administered, while the morphogenic output showed the typical trend effected by light only with one of the protein kinase inhibitors. Our data provide convincing evidence that protein phosphorylation plays a regulatory role in photocarotenogenesis and photomorphogenesis of Phycomyces. According to the model we propose, the putative signaling elements involved are anticipated to have a repressive function in the dark so that the responses are maintained in the "off" mode until the moment photon information has to flow through the regulatory circuit. Copyright 1999 Academic Press.