Differential effects of sulfate and chloride salinities on rice (Oryza sativa L.) gene expression patterns: A comparative transcriptomic and physiological approach

Abstract

Salinity is a challenge to rice production but most studies are dealing with NaCl and rarely consider Na2SO4 despite its importance in numerous areas of the world. To elucidate genome-level responses to chloride or sulfate salinity stress, seedlings from rice cv. IKP have been exposed for 48 h to two types of Na+-isostrength nutrient solution (NaCl 200 mM (EC18.84 dS m−1; Ψs = −0.983 MPa); and Na2SO4 100 mM (EC18.05 dS m−1; Ψs = −0.838 MPa)). A combined transcriptomic (microarray analysis) and physiological study was performed. NaCl was more toxic than Na2SO4 to rice seedlings. Contrasting genes were expressed under sulfate and chloride salinity, the difference being the most remarkable in root. Most of the genes involved in response to salt stress were up-regulated in Na2SO4-treated plants while more genes were down-regulated in NaCl-treated plants. Proline accumulated to a higher extent in NaCl-treated plants in relation to up-regulation of genes coding for Δ1-pyrroline-5-carboxylate synthetase and Ornithine-δ-aminotransferase which induced a higher activity of these enzymes in plants exposed to NaCl compared to Na2SO4. In contrast, sucrose accumulated in Na2SO4-treated plants while reducing sugars accumulated in NaCl-exposed ones. These differences could be explained by activities of sucrose-phosphate-synthase, sucrose synthase and acidic invertase but not by upregulation of the corresponding genes. Regulations of the expression of genes coding for signal sensing, perception and transduction and for transcription factors were completely different in response to NaCl and Na2SO4 suggesting that the nature of the counter anion is of primary importance in stress perception and plant response.

Keywords

• Ion toxicity
• NaCl
• Na2SO4
• Rice
• Salinity
• Salt stress