Salinity Stress-Mediated Suppression of Expression of Salt Overly Sensitive Signaling Pathway Genes Suggests Negative Regulation by Transcription Factor in .

Salt stress is one of the most serious threats in plants, reducing crop yield and production. The salt overly sensitive (SOS) pathway in plants is a salt-responsive pathway that acts as a janitor of the cell to sweep out Na ions. Transcription factors (TFs) are key regulators of expression and/or repression of genes. The basic leucine zipper (bZIP) TF is a large family of TFs regulating various cellular processes in plants. In the current study, we investigated the role of the TF in the regulation of SOS signaling pathway by measuring the transcript accumulation of its key genes such as , , and , in both wild-type (WT) and knock-out (KO) mutants under salinity stress. We further observed the activation of enzymatic and non-enzymatic antioxidant systems in the wild-type, (lacking catalase activity), and (lacking 9--epoxycarotenoid dioxygenase involved in the ABA pathway) KO mutants. Our findings revealed that plants exhibited an enhanced salt-sensitive phenotypic response similar to and compared to WT, 10 days after 150 mM NaCl treatment. Interestingly, the transcriptional levels of , , and increased significantly over time in the upon NaCl application, while they were downregulated in the wild type. We also measured chlorophyll a and b, pheophytin a and b, total pheophytin, and total carotenoids. We observed that the exhibited an increase in chlorophyll and total carotenoid contents, as well as proline contents, while it exhibited a non-significant increase in catalase activity. Our results suggest that negatively regulates the transcriptional events of pathway genes, and while modulating the antioxidant response to salt tolerance in .