Biosynthesis of chromophores for phytochrome and related photoreceptors

A broad group of open tetrapyrroles derived from heme are collectively called bilins. Phycocyanobilin and phycoerythrobilin are utilized as accessory chromophore for light harvesting by phycobiliproteins that comprise the photosynthetic apparatus in cyanobacteria and algae. Phytochromes, known as a major photoreceptor in plants, contain a phytochromobilin chromophore as an essential prosthetic group for photo-sensing. The possible ancestral proteins of phytochromes, as found in cyanobacteria and eubacteria, possess phycocyanobilin and/or biliverdin as a prosthetic group. In this mini-review, the diverse functions of bilin chromophores and their biosynthesis in photosynthetic organisms are summarized and the potential applications to plant biotechnology will be discussed.