Light-driven chlorophyll biosynthesis in angiosperms and the unique role of POR

NADPH:protochlorophyllide oxidoreductase (POR) is a key enzyme for the light-induced greening of etiolated angiosperm seedlings. In barley, one of the most intensively studied model systems known to date, two POR enzymes, termed PORA and PORB, co-exist in the prolamellar body of etioplasts. PORA and PORB form larger complexes dubbed LHPP, Light-Harvesting POR:Protochlorophllide complexes, that are involved in light trapping and excess light dissipation. Both PORA and PORB belong to the family of short-chain dehydrogenase/reductases comprising reductases, epimerases, and dehydrogenases., for which X-ray structures have been obtained. This allowed homology models to be constructed and tested by site-directed mutagenesis and has provided insights into the structure and functions of the PORA and PORB of barley and their unique roles during greening. It is the aim of the presentation to highlight the mechanisms that govern the biosynthesis, assembly and mode of action of the PORA and PORB and resulting LHPP complex in angiosperms.