2-oxoglutarate-dependent dioxygenases: A renaissance in attention for ascorbic acid in plants

Abstract

L-Ascorbic acid (ascorbate, Vitamin C) is an essential human micronutrient that is predominantly obtained from plants. It is known to work as the major antioxidant in plants, and it underpins several environmentally induced stresses due to its use as a co-factor by certain 2-oxoglutarate-dependent (2-OG) dioxygenases [2(OG)-dioxygenases]. It is important to understand the role of 2(OG)-dioxygenases in the biosynthesis of ascorbate. The present study examined contents of ascorbate and protein-protein interaction in nine T-DNA mutants of Arabidopsis containing an insert in their respective (2-OG) dioxygenase genes (At1g20270, At1g68080, At2g17720, At3g06290, At3g28490, At4g35810, At4g35820, At5g18900, At5g66060). In this study, the amount of ascorbate in five of the mutants was shown to be almost two-fold or more than two-fold higher than in the wild type. This result may be a consequence of the insertion of the T-DNA. The prediction of possible protein interactions between 2(OG)-dioxygenases and relevant ascorbate-function players may indicate the oxidative effects of certain dioxygenase proteins in plants. It is expected that certain dioxygenases are actively involved in the metabolic and biosynthetic pathways of ascorbate. This involvement may be of importance to increase ascorbate amounts in plants for human nutrition, and to protect plant species against stress conditions.

Fig 1. Standard curve for ascorbate dissolved in 1 ml of 0.1 M HCl and 1 mM EDTA.

Fig 2. The content of ascorbate in WT and nine mutant lines.

The values are expressed as means ± SE (n = 9), (P < 0.05). Means followed by the same letters within a column do not differ significantly from each other according to Duncan’s multiple range tests. FW denotes fresh weight.

Fig 3. A prediction of protein-protein links between respective dioxygenases and other ascorbate-related proteins in A. thaliana (http://string-db.org/).

Fig 4. A prediction of co-expression links between respective dioxygenase genes and other ascorbate-related genes in A. thaliana and other organisms (http://string-db.org/).