Prolamellar Body Formation by Light-Dependent NADPH: Protochlorophyllide Oxidoreductase (POR) From a Cyanobacterium Gloeobacter violaceus

Abstract

Etioplasts accumulate chlorophyll (Chl) precursors, protochlorophyllides (Pchlides), that form prolamellar body (PLB) as ternary complex with NADPH and POR. Previously, Reinbothe's group proposed that PLB is formed with two POR homologs, PORA and PORB, which respectively bind to Pchlide b and Pchlide a (the LHPP model). However, this model is still controversial, because other studies failed to detect presumably accumulated Pchlide b.
We previously reported that the kinetic properties of POR from a cyanobacterium Gloeobacter violaceus were similar to those of PORs from higher plants rather than a cyanobacterium Synechocystis sp. PCC6803. In this study, we introduced the Gloeobacter POR gene into the Arabidopsis PORA knockdown mutant, and showed that 1) Gloeobacter POR was fully functional in chloroplast biogenesis, and 2) it could form PLB. Given that cyanobacteria do not synthesize Chl b, our results do not support the LHPP model. Evolutionary implications of the enzyme will also be discussed.