Effects of nitric oxide on novel soybean cystatin gene expression under salt stress in soybean
Nitric oxide (NO) has been shown to orchestrate multiple defense responses to both abiotic and biotic stress. Importantly, elevation of nitric oxide content in plants by using nitric oxide generating compounds has been shown to enhance plant tolerance to abiotic stresses such as salt and drought via up-regulation of genes involved in the regulation of plant responses to abiotic stress. In this study, the effect(s) of nitric oxide (generated from 10 μM of the nitric oxide donor DET/NO) on the expression of a novel soybean cystatin gene (Glyma20g08800), lipid peroxidation, caspase-like activity and cell death in salt (150 mM)-stressed soybean leaves, roots and nodules were investigated. Salt treatment resulted in elevated lipid peroxidation, caspase-like activity and increased cell death in organs studied while the observed detrimental effects of salt stress were reversed by NO treatment. Salt stress suppressed the expression of Glyma20g08800 while the levels of expression of Glyma20g08800 returned towards those of unstressed plants when the salt-stressed plants were supplemented with nitric oxide (DETA/NO). Furthermore, promoter sequences of GmCYS1p626 and three of its homologues (Glyma20g08800, Glyma14g04250 and Glyma18g12240) were analyzed for putative abiotic stress and/NO cisregulatory elements based on co-expression analyses using bioinformatics. Several abiotic stress induced transcription factors (TFs) were identified and were hypothesized to be co-acting either directly or indirectly through additional factors in the regulation of soybean cystatin expression in response to NO and abiotic stress. Taken together, these results highlight the possibility of using NO to drive high levels of expression of cystatins during salt stress and lead to accumulation of the cystatin to levels that are sufficient to inhibit salt stress-induced caspase-like activity, which will inhibit salt stress-induced cell death and thus enhance the tolerance of the plant to salt stress and possibly tolerance to drought stress as well.