Loblolly pine (Pinus taeda L.) contains multiple expressed genes encoding light-dependent NADPH:protochlorophyllide oxidoreductase (POR)

Abstract

NADPH:protochlorophyllide oxidoreductase (POR) catalyzes the light-dependent reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), a key regulatory step in chlorophyll biosynthesis. In most angiosperms, POR is encoded by a small nuclear gene family, containing at least two differentially-expressed genes designated porA and porB. We have demonstrated that the PORs of loblolly pine (Pinus taeda L.), a gymnosperm, are encoded by a large multigene family, composed of two distinct subfamilies encoding porA and porB genes similar to those previously described in angiosperms. DNA gel blot analysis of genomic DNA showed that the two por subfamilies of loblolly pine have duplicated at different rates, with the porA subfamily containing two members, and the porB subfamily containing at least 11 potential members. DNA sequence analysis and gel blot hybridization studies also showed that a subset of the por genes present in the loblolly pine genome are pseudogenes. Based on the results of 5'- and 3'-RACE analysis, it appears that multiple porA and porB genes are expressed in loblolly pine cotyledons and stems during development. Using gene specific probes, no difference was observed in the steady-state levels of the different porA and porB transcripts in cotyledons of dark-grown seedlings before and following illumination. However, the steady state levels of the porA and porB transcripts were found to increase at different rates in the stems of dark-grown seedlings following illumination. The phylogenetic relationship between the por gene family members in P. taeda and other pine species and the potential significance of the two por subfamilies to the evolution of por gene function are discussed.