Overexpression of Protochlorophyllide Oxidoreductase C Regulates Oxidative Stress in Arabidopsis

Abstract

Light absorbed by colored intermediates of chlorophyll biosynthesis is not utilized in photosynthesis; instead, it is transferred to molecular oxygen, generating singlet oxygen (1O2). As there is no enzymatic detoxification mechanism available in plants to destroy 1O2, its generation should be minimized. We manipulated the concentration of a major chlorophyll biosynthetic intermediate i.e., protochlorophyllide in Arabidopsis by overexpressing the light-inducible protochlorophyllide oxidoreductase C (PORC) that effectively phototransforms endogenous protochlorophyllide to chlorophyllide leading to minimal accumulation of the photosensitizer protochlorophyllide in light-grown plants. In PORC overexpressing (PORCx) plants exposed to high-light, the 1O2 generation and consequent malonedialdehyde production was minimal and the maximum quantum efficiency of photosystem II remained unaffected demonstrating that their photosynthetic apparatus and cellular organization were intact. Further, PORCx plants treated with 5-aminolevulinicacid when exposed to light, photo-converted over-accumulated protochlorophyllide to chlorophyllide, reduced the generation of 1O2 and malonedialdehyde production and reduced plasma membrane damage. So PORCx plants survived and bolted whereas, the 5-aminolevulinicacid-treated wild-type plants perished. Thus, overexpression of PORC could be biotechnologically exploited in crop plants for tolerance to 1O2-induced oxidative stress, paving the use of 5-aminolevulinicacid as a selective commercial light-activated biodegradable herbicide. Reduced protochlorophyllide content in PORCx plants released the protochlorophyllide-mediated feed-back inhibition of 5-aminolevulinicacid biosynthesis that resulted in higher 5-aminolevulinicacid production. Increase of 5-aminolevulinicacid synthesis upregulated the gene and protein expression of several downstream chlorophyll biosynthetic enzymes elucidating a regulatory net work of expression of genes involved in 5-aminolevulinicacid and tetrapyrrole biosynthesis.

Cloning and functional characterization of PjPORB, a member of the POR gene family in Pseudosasa japonica cv. Akebonosuji

“…The leaf phenotypes were almost not distinguishable between PjPORBx plants and the WT (Fig. 3b, c), which was not consistent with the recent observation that AtPORC-overexpression led to greener leaf phenotype in AtPORCx Arabidopsis (Pattanayak and Tripathy 2011). And in comparison with the WT, some novel phenotypic changes were observed in PjPORBx Arabidopsis plants, such as the increased number of leaves per plant (at a similar age to the WT) and a delayed flowering (Fig.…”

“…3b, d). Despite these differences, PjPORBx Arabidopsis, similar to AtPORCx Arabidopsis (Pattanayak and Tripathy 2011), showed a mean reduction of 14 % in Pchlide content (Supplementary Table II) and was thereby indicative of its higher POR activity relative to the WT. It is well known that Pchlide acts as a potent photosensitizer and causes photo-damage to plants in excess light (Rebeiz et al 1988;Tripathy and Chakraborty 1991); and Pchlide regulates its own accumulation through feedback inhibiting the synthesis of its precursor, 5-aminolevulinicacid (ALA) (Stobart and Ameen-Bukhari 1984;Richter et al 2010).…”

“…Although the explanation for this observation is not clear, it is possible that PjPORBxoverexpression modulates gene expression and protein abundance of enzymes involved in Chl synthesis and, further, affects the metabolic flux of the Chl synthetic pathway, thereby leading to altered Chl a, Chl b, and total Chl synthesis. For example, there is an increasing body of evidence demonstrating that overexpression of PORC (Pattanayak and Tripathy 2011) and other Chl synthesisinvolved genes, like CHLM, CHLG, and CAO, co-modulates the expression of several other Chl synthetic genes (Alawady and Grimm 2005;Shalygo et al 2009). Moreover, it is also well known that plants coordinate development with crucial nutrients to ensure an adequate supply of materials and energy for successful completion of specific developmental programs (Lang 1952).…”

Salt‐stress induced modulation of chlorophyll biosynthesis during de‐etiolation of rice seedlings

“…This process involves interplay of chloroplast and nuclear genomes (Gray et al ). Chl biosynthesis in plants starts from amino acid, glutamic acid and involves many steps (Tripathy and Rebeiz , , Mohapatra and Tripathy , , Pattanayak and Tripathy , Pattanayak et al , Tanaka and Tanaka , Wu et al , Peter and Grimm , Shalygo et al , Pattanayak and Tripathy , Biswal et al ). It is known that chill, heat or drought stresses caused reduction in Chl biosynthesis during seedling stage which was due to downregulation of gene expression, protein abundance or posttranslational modification of several enzymes involved in tetrapyrrole metabolism (Tewari and Tripathy , , Le Lay et al , Sood et al , Mohanty et al , Dalal and Tripathy ).…”

Exogenous 5-Aminolevulenic Acid Promotes Seed Germination in Elymus nutans against Oxidative Damage Induced by Cold Stress

“…It is also known that ALA in low concentration regulates key physiological processes associated with plant growth under various abiotic and biotic stresses, including low or high temperature [7], [13], salinity [14], drought [15] and heavy metals [16]. In contrast, high levels of ALA can promote enhanced production of ROS, thereby enhancing oxidative stress in plants [17]. These results suggest that ALA has a great application potential in agricultural production as a new non-toxic endogenous substance [18].…”