Functional analysis of the nitrogenase-like protochlorophyllide reductase encoded in chloroplast genome using cyanobacterium leptolyngbya boryana

Abstract

Dark-operative protochlorophyllide (Pchlide) reductase (DPOR) is a nitrogenase-like enzyme consisting of two separable components, L-protein (a ChlL dimer) and NB-protein (a ChlN-ChlB heterotetramer), which are structural counterparts of Fe protein and MoFe protein of nitrogenase, respectively. In contrast to the limited distribution of nitrogenase only among prokaryotes, DPOR is distributed among not only photosynthetic prokaryotes but also eukaryotic phototrophs such as green algae, moss, ferns and gymnosperms. While prokaryotic DPORs have been characterized, there has very little study on eukaryotic DPOR functioning in the chloroplast. The three structural genes of DPOR, chlL, chlN and chlB, are encoded by the chloroplast DNA. Recently we have established an in-vivo complementation system using mutants lacking DPOR genes of the cyanobacterium Leptolyngbya boryana to examine whether DPOR genes are functional. We applied this system to evaluate the probable DPOR genes encoded by the chloroplast DNAs from the moss Physcomitrella patens and black pine Pinus thunbergii. We discuss the functional operation of DPOR in the chloroplasts of these photosynthetic eukaryotes.