Characterization of a novel soybean candidate glutathione peroxidase/thioredoxin-dependent peroxidase under salt stress

>Magister Scientiae - MScThe production of reactive oxygen species (ROS) is prominent in all aerobic metabolisms including plants. For this reason, the redox homeostasis of the production and scavenging of these intermediates is imperative for growth, development and survival during unfavourable conditions. In this study, a putative glutathione peroxidase gene (Glyma17g34110) from Glycine max (soybean) was identified and analyzed. The successful characterisation of Glyma17g34110 provided evidence of it being a glutathione peroxidase using glutathione as its preferred electron donor and substrate. Furthermore, it is known that antioxidant enzymes such as GPX exist in various tissues, performing a diverse set of functions. By a bioinformatic analysis of Glyma17g34110 and its promoter region, it was indicated that Glyma17g34110 could be a putative chloroplast protein that could play an important role in photosynthesis.One of the major factors affecting plant growth and development worldwide is abiotic stresses such as salinity. In the presence of salinity the production of harmful ROS is increased, resulting in detrimental reactions with important biological features (DNA, protein and lipid membranes), leading to cell death. The analysis of Glyma17g34110 under salt stress revealed that it is a salt sensitive gene and thus, the down-regulation of Glyma17g34110 could be due to the lack of known defence and response cis-acting elements present in the promoter region. Furthermore, it was proven in previous studies that the application of exogenous nitric oxide (NO) increases the activity of antioxidant enzymes. In this thesis it was observed that the presence of exogenously applied NO increased the expression of Glyma17g34110 tremendously in all soybean tissues (leaves, roots and nodules) investigated.Studies have found numerous cis-acting elements to be NO responsive, however, none of these elements were found in the promoter region upstream of glyma17g34110. This suggests that novel cis-acting elements could be present in the promoter region of Glyma17g34110.Thus, increasing the expression of Glyma17g34110 during salinity in the presence of NO, as well as the identification of these novel cis-acting elements, could lead to the enhancement of the defence mechanisms against ROS, which could lead to increasing plant tolerance to stress