Salinity Stress-Mediated Suppression of Expression of Salt Overly Sensitive Signaling Pathway Genes Suggests Negative Regulation by AtbZIP62 Transcription Factor in Arabidopsis thaliana

Abstract

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 Arabidopsis thaliana bZIP62 TF in the regulation of SOS signaling pathway by measuring the transcript accumulation of its key genes such as SOS1, 2, and 3, in both wild-type (WT) and atbzip62 knock-out (KO) mutants under salinity stress. We further observed the activation of enzymatic and non-enzymatic antioxidant systems in the wild-type, atbzip62, atcat2 (lacking catalase activity), and atnced3 (lacking 9-cis-epoxycarotenoid dioxygenase involved in the ABA pathway) KO mutants. Our findings revealed that atbzip62 plants exhibited an enhanced salt-sensitive phenotypic response similar to atnced3 and atcat2 compared to WT, 10 days after 150 mM NaCl treatment. Interestingly, the transcriptional levels of SOS1, SOS2, and SOS3 increased significantly over time in the atbzip62 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 atbzip62 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 AtbZIP62 negatively regulates the transcriptional events of SOS pathway genes, AtbZIP18 and AtbZIP69 while modulating the antioxidant response to salt tolerance in Arabidopsis.

Insights into the Transcriptional Regulation of Branching Hormonal Signaling Pathways Genes under Drought Stress in Arabidopsis

“…The results revealed the presence cis- regulatory elements specific to the AtbZIP18 and AtbZIP69 , among others ( Table 1 ). These two bZIP TFs were selected because their expression was recently suggested to be negatively regulated by the AtbZIP62 TF in response to salt stress [ 28 ]. These results would imply that the AtbZIP62 TF may interact with the AtbZIP18 and/or AtbZIP69 in order to regulate the transcription of each of the target branching genes.…”

“…The bZIP transcription factors are said to either operate alone or in complex with other bZIP TFs to regulate the expression of their target genes. In a recent study, the AtbZIP18 and AtbZIP69 were proposed to be negatively regulated by AtbZIP62 in response to salt stress [ 28 ]. Similarly, our data show that the expression of AtbZIP18 and AtbZIP69 were upregulated in the atzip62 , while showing a downregulation pattern in Col-0 wild type ( Figure 2 O,P).…”

“…The results of the transcription factors binding sites prediction did not detect any specific cis- regulatory element of the AtbZIP62 TF in the promoter regions of the target genes. Rather, we detected cis- regulatory element of two other bZIP TF ( AtbZIP18 and AtbZIP69 ) among others, which have been reported to be negatively regulated by the AtbZIP62 TF in response to salinity stress [ 28 ]. Similarly, data shown in the panels O and P of Figure 2 revealed that the expression of AtbZIP18 and AtbZIP69 TFs was significantly upregulated by drought stress in the atbzip62 knockout plants, but downregulated in the Col-0 WT.…”

“…In this perspective, we monitored by qPCR the transcripts accumulation of auxin carriers (PIN-FORMED protein) encoding genes, strigolactone biosynthetic genes (more axillary branching, MAX), gibberellic acid (GA) biosynthetic genes, and cytokinin (CK) biosynthetic genes (isopentenyltransferase, IPT) in Arabidopsis Col-0 wild type under drought stress conditions. In addition, in order to explore the transcriptional interplay of the target genes with the AtbZIP62 TF, their expression levels were analyzed in the atbzip62 knockout plants (lacking the AtbZIP62 gene recently suggested to be involved in the adaptive response towards drought [ 27 ] and salinity [ 28 ] tolerance) compared to the Col-0 wild type (WT). Moreover, the phenotype of atbzip62 plants was examined under normal growth conditions.…”

Regulation Mechanisms of Plant Basic Leucine Zippers to Various Abiotic Stresses

“… Tang W. et al (2012) found that heterologously expressing Arabidopsis thaliana AtbZIP60 could increase salt resistance and superoxide dismutase activity of tobacco, rice, and Pinus elliottii . Recently, Rolly et al (2020) found that AtbZIP62 negatively regulated the transcriptional SOS signaling pathway genes and thus negatively regulates the salt tolerance of Arabidopsis. In Glycine max , overexpression of the GmbZIP1 enhances salt tolerance in transgenic plants ( Gao et al, 2011 ).…”