Arabidopsis light-dependent protochlorophyllide oxidoreductase A (PORA) is essential for normal plant growth and development

During skotomorphogenesis in angiosperms, NADPH:protochlorophyllide oxidoreductase (POR) forms an aggregate of photolabile NADPH-POR-protochlorophyllide (Pchlide) ternary complexes localized to the prolamellar bodies within etioplasts. During photomorphogenesis, POR catalyzes the light-dependent reduction of Pchlide a to chlorophyllide (Chlide) a, which is subsequently converted to chlorophyll (Chl). In Arabidopsis there are three structurally related POR genes, denoted PORA, PORB and PORC. The PORA and PORB proteins accumulate during skotomorphogenesis. During illumination, PORA is only transiently expressed, whereas PORB and PORC persist and are responsible for bulk Chl synthesis throughout plant development. Here we have tested whether PORA is important for skotomorphogenesis by assisting in etioplast development, and normal photomorphogenic development. Using reverse genetic approaches, we have identified the porA-1 null mutant, which contains an insertion of the maize Dissociation transposable element in the PORA gene. Additionally, we have characterized PORA RNAi lines. The porA-1 and PORA RNAi lines display severe photoautotrophic growth defects, which can be partially rescued on sucrose-supplemented growth media. Elimination of PORA during skotomorphogenesis results in reductions in the volume and frequency of prolamellar bodies, and in photoactive Pchlide conversion. The porA-1 mutant characterization thus establishes a quantitative requirement for PORA in etioplast development by demonstrating significant membrane ultrastructural and biochemical defects, in addition to suggesting PORA-specific functions in photomorphogenesis and plant development.