Molecular Cloning and Expression of Sequence Variants of Manganese Superoxide Dismutase Genes from Wheat

Authors: BAEK, KWANG-HYUN - Yeungnam University; Skinner, Daniel

Submitted to: The Korean Society of Environmental Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2010
Publication Date: 3/31/2010
Citation: Baek, K., Skinner, D.Z. 2010. Molecular Cloning and Expression of Sequence Variants of Manganese Superoxide Dismutase Genes from Wheat. Korean Journal of Environmental Agriculture. 29(1):77-85.

Interpretive Summary: Superoxide dismutase (SOD) Is an enzyme that detoxifies reactive oxygen species, forms of oxygen that are generated in plant cells under stressful conditions, that can damage cellular components. Multiple genes that encode SOD and differ slightly from one another are found in wheat. In this study, three different wheat SOD genes were expressed in a mutant bacterial strain that does not express SOD on its own. One of the SOD genes expressed active enzyme when the bacterial strain was grown and 37°C, another gene expressed active SOD only when grown at 22°C, and the third did not express active SOD under any of the experimental conditions tested. These results indicated that different wheat SOD genes probably are activated under different conditions, suggesting the SOD stress response is controlled at the level of specific genes activation. Elucidation of the mechanisms controlling this phenomenon will lead to greater understanding of stress response mechanisms in crop plants and new approaches to breeding for stress tolerance.

Technical Abstract: Reactive oxygen species (ROS) are very harmful to living organisms due to the potential oxidation of membrane lipids, DNA, proteins, and carbohydrates. Transformed E.coli strain QC 871, superoxide dismutase (SOD) double-mutant, with three sequence variant MnSOD1, MnSOD2, and MnSOD3 manganese superoxide dismutase (MnSOD) gene isolated from wheat. Although all QC 871 transformants grown at 37 ' expressed mRNA of MnSOD variants, only MnSOD2 transformant had functional SOD activity. MnSOD3 expressed active protein when grown at 22', however, MnSOD1 did not express functional protein at any growing and induction conditions. The sequence comparison of the wheat MnSOD variants revealed that the only amino acid difference between the sequence MnSOD2 and sequences MnSOD1 and 3 is phenylalanine/serine at position 58 amino acid. We made MnSOD2S58F gene, which was made by altering the phenylalaine to serine at position 58 in MnSOD2. The expressed MnSOD2S58F protein had functional SOD activity, even at higher levels than the original MnSOD2 at all observed temperatures. These data suggest that amino acid variation can result in highly active forms of MnSOD and the MnSOD2S58F gene can be an ideal target used for transforming crops to increase tolerance to environmental stresses.