CpcF-dependent regulation of pigmentation and development in Fremyella diplosiphon

Cyanobacteria harvest light for photosynthesis using photosynthetic light-harvesting complexes called phycobilisomes (PBSs). Lyases are enzymes responsible for covalent attachment of light-absorbing chromophores to the phycobiliproteins (PBPs) contained in PBSs. We isolated a pigmentation mutant in the filamentous cyanobacterium Fremyella diplosiphon and determined that it possesses an insertional mutation in cpcF, which encodes one component of a heterodimeric phycocyanin lyase. Here, we discuss the implications of the mutation in cpcF on light-dependent pigmentation and morphology responses characteristic of complementary chromatic adaptation in F. diplosiphon. Although cpcF encodes a phycocyanin lyase, significant decreases in the levels of all classes of PBPs are associated with CpcF deficiency in F. diplosiphon. Notably, CpcF deficiency has a limited effect on the shape of F. diplosiphon cells, but significantly impacts filament length. Possible mechanisms for the broad impact of CpcF deficiency on pigmentation and filament morphology are discussed.