Comparative Analysis of Salinity Responsive Candidate Gene Expression in Selected Sri Lankan Rice Varieties

Abstract

Studying of expression dynamics of salt responsive candidate genes under different genetic background of rice is important to develop resilient salt tolerant rice varieties. The present study was focused to assess the comparative expression of salinity responsive genes which are involved in Na+/K+ homeostasis (OsNHX1), signal transduction pathway (OsMAPK5, OsCDPK7) and synthesis of osmoprotectant (OsTPS1). Comparative expression of selected genes were assessed in At354 (improved), Godawee (traditional) and Kuruwi Perunel (traditional), salinity tolerant varieties and Suwandel, a salinity susceptible traditional variety. The assessment was done before salinization (at 0 h) and after salinization at 24 h and 72 h using semi-quantitative Reverse Transcriptase PCR (RT-PCR). RT-PCR products were analysed using 1.5% agarose gel electrophoresis. Resulted gel profiles were assessed and relative level of gene expression was measured based on the intensity of the PCR product in terms of average pixel values. Relative level of gene expression in four varieties was plotted against the exposure time to salinity. Accordingly, marked variation in expression pattern of the selected genes was detected in four varieties over the tested in Godawee and Suwandel compared to At354 and Kuruwi Perunel. At 24 h, all four genes were up-regulated in At354 and Godawee while they were down-regulated in Suwandel. In Kuruwi Perunel, OsNHX1, OsMAPK5 and OsCDPK7 genes were up-regulated at 24 h while OsTPS1 was up-regulated at 72 h. At 72 h, continuous expression of all genes was observed in Kuruwi Perunel and Godawee, whereas expression was comparatively down-regulated in At354 approximately to the same level under non-stress condition. It could be suggested that At354 might have been adapted to the stress relatively earlier compared to Godawee and Kuruwi Perunel, where expressions of genes were less pronounced. Further experiments with various time period of salinity exposure should be carried out to make detailed inference regarding the expression dynamics in tested rice varieties.