Abstract
Dark-operative protochlorophyllide reductase (DPOR) is a nitrogenase-like enzyme consisting of two components L-protein (ChlL) and NB-protein (ChlN-ChlB) and plays a critical role in chlorophyll (Chl) biosynthesis in the dark. All subunits of DPOR are encoded in plastid genome in photosynthetic eukaryotes. RNA editing in chlN and chlB, which is required for the restoration of codons for evolutionarily conserved amino acid residues, was reported in some gymnosperms. Here we report that RNA editing regulates the DPOR activity in black pine Pinus thunbergii. We constructed a series of shuttle vectors to express P. thunbergii chlN-chlB with and without mutations responsible for the RNA editing, and introduced them into the mutants lacking chlB of the cyanobacterium Leptolyngbya boryana. Only the transformants carrying the edited chlN-chlB genes restored the ability of Chl biosynthesis in the dark. Biochemical analysis of the cyanobacterial NB-protein with site-directed mutations responsible for the RNA editing supported the in-vivo complementation result. These results suggested that RNA editing regulates the greening in the dark through the NB-protein activity in P. thunbergii.
