Ferredoxin-dependent bilin reductases in eukaryotic algae: Ubiquity and diversity

Abstract

Linear tetrapyrroles (bilins) are produced from heme by heme oxygenase, usually forming biliverdin IXα (BV). Fungi and bacteria use BV as chromophore for phytochrome photoreceptors. Oxygenic photosynthetic organisms use BV as a substrate for ferredoxin-dependent bilin reductases (FDBRs), enzymes that produce diverse reduced bilins used as light-harvesting pigments in phycobiliproteins and as photoactive photoreceptor chromophores. Bilin biosynthesis is essential for phototrophic growth in Chlamydomonas reinhardtii despite the absence of phytochromes or phycobiliproteins in this organism, raising the possibility that bilins are more generally required for phototrophic growth by algae. We here leverage the recent expansion in available algal transcriptomes, cyanobacterial genomes, and environmental metagenomes to analyze the distribution and diversification of FDBRs. With the possible exception of euglenids, FDBRs are present in all photosynthetic eukaryotic lineages. Phylogenetic analysis demonstrates that algal FDBRs belong to the three previously recognized FDBR lineages. Our studies provide new insights into FDBR evolution and diversification.

Cyanobacteriochrome-based photoswitchable adenylyl cyclases (cPACs) for broad spectrum light regulation of cAMP levels in cells

“…The successful manipulation of cAMP in vivo by cPAC shows that this protein is a viable platform for optogenetic tool applications in a wide variety of photosynthetic species where reduced bilins, also known as phytobilins, are present. These not only includes cyanobacteria, but also eukaryotic algae and plants (70). We envisage considerable utility of this tool for light-dependent reprogramming of plastid metabolic pathways in chlorophyte algae such as Chlamydomonas reinhardtii, due to its ability to produce PCB despite its lack of bilin-based sensors in the phytochrome family (71).…”

Amoeba Genome Reveals Dominant Host Contribution to Plastid Endosymbiosis

“…3 C ). FDBRs are involved in the breakdown of heme to different bilins that act as chromophores for light-harvesting (phycobiliproteins) and/or light-sensing functions (phytochromes; Rockwell and Lagarias 2017 ). It is interesting that bilin biosynthesis is present in all oxygenic photosynthetic lineages, regardless of the existence of phytochromes or phycobiliproteins ( Rockwell et al.…”

Phytochrome evolution in 3D: deletion, duplication, and diversification

“…b), and most cryptophytes contain only PEBA and PEBB. Some cryptophytes also contain PCYA derived from Cyanidioschyzon PCYA (Rockwell & Lagarias, ), but such cryptophytes do not form a clade. Therefore, either a subset of mesophilic cryptophytes acquired PCYA from Cyanidioschyzon via two or more HGT events, or all three FDBRs were present in the ancestor to the cryptophyte plastid.…”

“…PCB is also used by some bacterial phytochromes (Yeh et al , ; Jaubert et al , ), including cyanobacterial ones, but these organisms use the FDBR PcyA rather than HY2. FDBRs are ubiquitous in photosynthetic eukaryotes (Rockwell & Lagarias, ), with other family members (PEBA and PEBB) producing phycoerythrobilin for use in bilin‐based light‐harvesting systems (Glazer, ; Frankenberg et al , ). Eukaryotic PCYA enzymes are found in glaucophyte, prasinophyte, and chlorophyte algae, defined as in (Duanmu et al , ), as well as some rhodophytes and cryptophytes (see Section III).…”