Detection of novel key residues of MnSOD enzyme and its role in salinity management across species

Abstract

Every living organism is persistently exposed to stress from its surrounding ecosystem throughout its life. Salinity is one such abiotic stress, which enforces natural boundaries on caloric and nutritional potential of agricultural yield and considered as a major impediment to global food security, due to the accumulation of salt in water or soil medium hampering the growth of the organisms living in that medium (Hussain et al. 2010 ). Salinity inhibits growth and development of plants by imposing osmotic stress that leads to limitation in water uptake and chemical stress by ion disequilibrium (Abogadallah 2010). In such extreme conditions, certain plants survive in dormant stage during stress condition, while a few tolerate it by developing some avoidance mechanism and morphological changes (Flowers et al.1986). The plants incapable of coping with salinity are known as salt-sensitive plants (glycophytes), whereas the plants (around 2%) that can cope with high salinity are referred as halophytes (Glenn and Brown 1999). One of the major biochemical changes that occur inside the cells during salt stress is the overproduction of reactive oxygen species (ROS; Rahnama and Ebrahimzadeh 2006). Salt stress limits the gas exchange phenomena, which ultimately reduce the CO2 supply to leaves. This leads to the production of more ROS due to reduction of the photosynthetic electron transport chain (Ashraf 2009). In turn, excess ROS produced cause damage to proteins, lipids and DNA, leading to cell death by protein denaturation, lipid peroxidation and DNA mutation, respectively (Alscher et al.2002). Superoxide dismutase (SOD) is one of the antioxidative enzymes, as the first line defence against ROS by dismutating superoxide radicals to hydrogen peroxide (H2O2), which prevents consequent damage to cell by superoxide radicals (Alscher et al.2002). Wanget al.(2007) reported that overexpression of MnSOD reduces the cellular damage caused by ROS in tomato plants. Meloniet al.(2003) reported that increasing the expression of SOD protects cotton plants against salt stress. Though, a number of studies have examined the expression of MnSOD, an accurate prediction of the function of this protein through structural analysis across species is not yet performed. This may be due to availability of limited number of tertiary structures in Protein Data Bank (PDB),especially in plant species. Therefore, in this study, an in silico approach has been followed to identify and analyse the probable key residues of MnSOD enzyme responsible for saltstress tolerance mechanism across species.