Salt-Specific Gene Expression Reveals Elevated Auxin Levels in Arabidopsis thaliana Plants Grown Under Saline Conditions

Abstract

Soil salinization is increasing globally, driving a reduction in crop yields that threatens food security. Salinity stress reduces plant growth by exerting two stresses on plants: rapid shoot ion-independent effects which are largely osmotic and delayed ionic effects that are specific to salinity stress. In this study we set out to delineate the osmotic from the ionic effects of salinity stress. Arabidopsis thaliana plants were germinated and grown for two weeks in media supplemented with 50, 75, 100, or 125 mM NaCl (that imposes both an ionic and osmotic stress) or iso-osmolar concentrations (100, 150, 200, or 250 mM) of sorbitol, that imposes only an osmotic stress. A subsequent transcriptional analysis was performed to identify sets of genes that are differentially expressed in plants grown in (1) NaCl or (2) sorbitol compared to controls. A comparison of the gene sets identified genes that are differentially expressed under both challenge conditions (osmotic genes) and genes that are only differentially expressed in plants grown on NaCl (ionic genes, hereafter referred to as salt-specific genes). A pathway analysis of the osmotic and salt-specific gene lists revealed that distinct biological processes are modulated during growth under the two conditions. The list of salt-specific genes was enriched in the gene ontology (GO) term “response to auxin.” Quantification of the predominant auxin, indole-3-acetic acid (IAA) and IAA biosynthetic intermediates revealed that IAA levels are elevated in a salt-specific manner through increased IAA biosynthesis. Furthermore, the expression of NITRILASE 2 (NIT2), which hydrolyses indole-3-acetonitile (IAN) into IAA, increased in a salt-specific manner. Overexpression of NIT2 resulted in increased IAA levels, improved Na:K ratios and enhanced survival and growth of Arabidopsis under saline conditions. Overall, our data suggest that auxin is involved in maintaining growth during the ionic stress imposed by saline conditions.

A dual-flow RootChip enables quantification of bi-directional calcium signaling in primary roots

“…Based on former literature that observed Ca 2+ signaling in response to NaCl treatment, 100 mM NaCl was chosen for the presented experiments ( Choi et al., 2014 ; Stanley et al., 2018 ). Effects of 100 mM NaCl treatment on Arabidopsis has been well studied in the past, which allows integration of our insights into the existing knowledge ( Yang et al., 2019 ; Cackett et al., 2022 ). PEG-6000 is known to induce drought stress via lowering plants water potential as a result of osmotic stress ( Sevindik et al., 2022 ).…”

A genome‐wide association study identifies novel players in Na and Fe homeostasis in Arabidopsis thaliana under alkaline‐salinity stress

“…Physical interaction between AtALA3 and two ARFGEFs (ADPribosylation factor GTPases) ‐ BIG3 (Brefeldin A‐Inhibited Guanine Nucleotide‐Exchange Protein3) and GNOM, which is essential for proper trafficking of PIN auxin transporters – has been observed in endomembrane, thus regulating trafficking events in the late secretory pathway and ala3 mutants are defective in auxin mediated developmental processes (Zhang et al., 2020 ). There is increasing evidence for a role of auxin in plant response to both the Fe deficiency (Celletti et al., 2020 ) and salinity (Cackett et al., 2022 ). Plant P4 ATPases are expected to have a major role in any physiological process involving lipid signaling, vesicle formation and/or lipid‐dependent protein recruitment to membranes.…”

Do Opposites Attract? Auxin-Abscisic Acid Crosstalk: New Perspectives

“…However, the stimuli that induce WRKY41 are not yet clear, and their elucidation might reveal new interactions. PIN3 expression is also directly inhibited by HAT2, an HD-Zip II transcription factor, whose expression is upregulated by osmotic stress, at least in roots, thus inhibiting meristem growth [ 185 ], and its expression is also downregulated in response to NaCl [ 186 ], but the exact mechanism remains uncertain. Auxin-ABA interactions remain particularly understudied in relation to cold responses, which are mediated by ABA [ 187 ].…”