Evolutionary Selection of Phytochrome Chromophores

Abstract

Phytochromes in plants are dimeric proteins that have a single linear tetrapyr- role molecule, phytochromobilin (PΦB), as chromophore in each protein mole- cule. Chromophore attachment to photoreceptor is essential for light perception. Although different types of phytochromes are encoded by a small multigene family in plants, the structure of chromophore molecules is common for all phy- tochromes. In prokaryotes, phytochrome-like proteins named bacteriophy- tochromes (Bphs), which have a different prosthetic group, biliverdin (BV)or phycocyanobilin (PCB), were discovered in the 1990s ([Hughes and Lamparter 1999], [Montgomery and Lagarias 2002]). The genes and proteins for tetrapyrrole metabolism have been identified in plants by a molecular genetic approach with Arabidopsis photomorphogenic mutants ([Muramoto et al 1999], [Kohchi et al 2001])and in algae by a comparative genomics ([Frankenberg et al 2001]). Using mutants and biosynthetic genes of phytochrome chromophores as tools, a genetic system was developed allowing a structure-function assay of phytochrome chro- mophores in photochromic and physiological responses in plants ([Kami et al 2004]). Here we present a mini-review of phytochrome chromophore biosynthe- sis and structure from an evolutionary point of view.