Cloning, Structural and Expression Analysis of OsSOS2 in Contrasting Cultivars of Rice under Salinity Stress

Salinity is one of the major environmental factors limiting growth and productivity of crop plants in coastal areas and irrigated farmlands. Salinity tolerance is a very complex trait. Plants adapt to salinity stress by coordinated and orchestrated functioning of various complex mechanisms. In Arabidopsis thaliana, SOS (Salt Overly Sensitive) pathway has been established as a major player in ion homeostasis and salt tolerance. The SOS pathway has recently been shown to be conserved in rice as well. In the present study, we have isolated and characterized the OsSOS2 full-length cDNA from a salt sensitive Oryza sativa L. cv ‘IR64’, which encodes 50.65 KD protein. It was observed that OsSOS2 transcripts are induced by salinity and further showed differential accumulation at different time intervals at seedling stage in contrasting cultivars of rice i.e. ‘IR64’ (salt sensitive) and ‘Pokkali’ (naturally salt tolerant). We have also observed tissue specific expression for OsSOS2 in field grown mature plants of these contrasting cultivars. With the use of molecular modeling techniques, we have modeled OsSOS2 protein and present a comparative structural analysis with respect to its ortholog from model plant Arabidopsis thaliana. Comparison of various orthologous sequences has shown high level of similarities between SOS2 members isolated from Arabidopsis thaliana and O. sativa. Experiments have established that the SOS3 protein senses Ca and regulates SOS2 activity. Therefore, we have carried out the analysis of conserved binding site for SOS3 protein in SOS2 protein which can give an insight to the probable mechanism of the functioning of OsSOS2 protein. We propose that OsSOS2 is one of the important members of salinity stress response in rice functioning towards ion homeostasis. _____________________________________________________________________________________________________________