Identification of two differentially regulated isoforms of protochlorophyllide oxidoreductase (POR) from tobacco revealed a wide variety of light- and development-dependent regulations of POR gene expression among angiosperms

NADPH-protochlorophyllide oxidoreductase (POR) catalyzes the light-dependent reduction of protochlorophyllide a in the chlorophyll biosynthetic pathway. Here, we identified two distinct POR cDNAs from tobacco. Both POR isoforms are encoded by a respective single copy gene in tobacco genome. The overall deduced amino acid sequences of two tobacco cDNAs, designated here POR1 and POR2, displayed significant identities (similar to75%), but showed different patterns of light and developmental regulation. In contrast to the previously isolated POR isoforms of Arabidopsis thaliana and barley, the expression of both tobacco POR isoforms were not negatively regulated by light and persisted in matured green tissues. Furthermore, the expression of both genes appeared to be regulated by a diurnal regulation. These results show a wide variety of light- and development-dependent regulations of POR gene expression among angiosperms. Furthermore, phylogenetic analysis including tobacco revealed that POR gene family is differentially represented by angiosperms, most of which is probably caused by independent gene duplication in individual plant. Present results imply a modification of the previous concept that chlorophyll biosynthesis and chloroplast differentiation in angiosperms are ubiquitously controlled by unique functions of two POR isoforms.