Arabidopsis protochlorophyllide oxidoreductase A (PORA) restores bulk chlorophyll synthesis and normal development to a porB porC double mutant

Abstract

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.

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

“…To assess the ability of PORA to direct bulk Chl biosynthesis independent of PORB and PORC, a PORA cDNA was ectopically expressed in the porB-1 porC-1 double mutant background, thereby rescuing the double mutant impaired growth and Chl-deficient phenotypes. This demonstrates the clear ability of ectopically expressed PORA to function as the only POR required for bulk Chl synthesis (Paddock et al 2010).…”

“…To determine the genotypes of individual plants grown on MS agar, total DNA was analyzed by PCR (Paddock et al 2010), with appropriate oligonucleotide primers to test for the presence of the respective Ds element and the intact wild-type POR genomic sequence. Primer sequences including DS5 are included in Supplementary Figure 1 and Frick et al (2003).…”

GROWTH REGULATING FACTOR5 Stimulates Arabidopsis Chloroplast Division, Photosynthesis, and Leaf Longevity

“…PORA is mainly active in etiolated seedlings after illumination, which is consistent with the lack of expression in wild-type developing leaves. However, overexpression of PORA rescues Chl levels and the photoautotrophic development of porB porC double mutant plants (Frick et al, 2003;Paddock et al, 2010). The observed higher Chl accumulation in GRF5-overexpressing plants, therefore, likely results from the strong up-regulation of PORA at the end of the transition and expansion phases of leaf development.…”

Cell Growth Defect Factor1/CHAPERONE-LIKE PROTEIN OF POR1 Plays a Role in Stabilization of Light-Dependent Protochlorophyllide Oxidoreductase in Nicotiana benthamiana and Arabidopsis

“…There are varying numbers of POR genes depending on the species: Among angiosperms, tobacco (Nicotiana tabacum) has two POR genes, POR1 and POR2 (Masuda et al, 2002), whereas Arabidopsis has three POR genes, PORA, PORB, and PORC, which show different expression profiles (Frick et al, 2003;Masuda et al, 2003;Masuda and Takamiya, 2004;Paddock et al, 2010). Arabidopsis PORA mRNA and protein are both detected abundantly in etiolated seedlings, but their levels dramatically decrease upon illumination.…”