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.
Highlights
Soil salinity is considered as the second most widespread soil problem causing the significant reduction in productivity of global rice cultivation (Gregorio et al, 1997; Ashraf and O’Leary, 1996; Munns et al, 2006)
Two traditional salt tolerant local rice varieties, i.e. Kuruwi Perunel (IRGC Ac No: 8994) and Godawee (IRGC Ac No 15653), one traditional salt susceptible local variety, Suwandel (IRGC Ac No 31552) obtained from International Rice Research Institute (IRRI) and salt tolerant improved variety, At354 collected from Rice Research and Development Institute (RRDI), Batalagoda, Sri Lanka were used for the present study based on the assessment of salt tolerance in our previous studies
With respect to the expression of OsNHX1 gene, At354 and Kuruwi Perunel exhibited relatively low level of gene expression under non-stress condition compared to Godawee and Suwandel (Figure 1 and Figure 2)
Summary
Soil salinity is considered as the second most widespread soil problem causing the significant reduction in productivity of global rice cultivation (Gregorio et al, 1997; Ashraf and O’Leary, 1996; Munns et al, 2006). Salinity tolerance in rice is a complex mixture of mopho-physiological traits, which is controlled by multiple genes (Chinnusamy et al, 2005). Ismail et al (2007) has reported that in rice most salt-tolerant genotypes are superior in only one or a few of these traits and there is a potentiality to pyramid superior alleles for all useful mechanisms into one rice genotype towards producing resilient salt tolerant varieties (Ismail et al, 2007). It is essential to understand the fundamental molecular mechanisms behind stress tolerance in plants. Considerable progress towards understanding the molecular basis of salt tolerance in rice has been made during the last two decades and number of genes involved in signal transduction, transcription regulation, ion transporters and metabolic pathways, conferring salt tolerance in rice have been isolated (Ismail et al, 2007; Kumar et al, 2013)
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