Arabidopsis protochlorophyllide oxidoreductase A (PORA) restores bulk chlorophyll synthesis and normal development to a porB porC double mutant
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In angiosperms the strictly light-dependent reduction of protochlorophyllide to chlorophyllide is catalyzed by NADPH:protochlorophyllide oxidoreductase (POR). The Arabidopsis thaliana genome encodes three structurally related but differentially regulated POR genes, PORA, PORB and PORC. PORA is expressed primarily early in development—during etiolation, germination and greening. In contrast, PORB and PORC are not only expressed during seedling development but also throughout the later life of the plant, during which they are responsible for bulk chlorophyll synthesis. The Arabidopsis porB-1 porC-1 mutant displays a severe xantha (highly chlorophyll-deficient) phenotype characterized by smaller prolamellar bodies in etioplasts and decreased thylakoid stacking in chloroplasts. Here we have demonstrated the ability of an ectopic PORA overexpression construct to restore prolamellar body formation in the porB-1 porC-1 double mutant background. In response to illumination, light-dependent chlorophyll production, thylakoid stacking and photomorphogenesis are also restored in PORA-overexpressing porB-1 porC-1 seedlings and adult plants. An Arabidopsis porB-1 porC-1 double mutant can therefore be functionally rescued by the addition of ectopically expressed PORA, which suffices in the absence of either PORB or PORC to direct bulk chlorophyll synthesis and normal plant development.
KeywordsNADPH:protochlorophyllide oxidoreductase PORA PORB PORC Prolamellar body Photomorphogenesis Chlorophyll
We thank Rosario Barbieri for her advice, Rebecca Lamb and Patrice Hamel for their comments, Kathy Wolken at The Ohio State University Campus Microscopy and Imaging Facility for assistance with the electron microscopy, Dick Sayre for providing access to the fluorescence spectrophotometer, and the Nottingham Arabidopsis Stock Centre (Nottingham, UK) and The Arabidopsis Biological Resource Center (Columbus, OH, USA) for the generous donation of seed lines.
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