Arabidopsis Antiporter Genes as Targets of NO Signalling: Phylogenetic, Structural, and Expression Analysis

Nitric oxide is a gaseous signalling molecule produced by plants. Slight changes in endogenous NO levels have significant biochemical and physiological consequences. We investigated the structural and functional properties of NO-responsive antiporter genes in <i>Arabidopsis thaliana</i>. Phylogenetic analysis of 50 antiporter genes classified them into four subgroups based on the presence of NHX and CPA domains and the evolutionary similarity of the protein sequences. Antiporters were found scattered across the five chromosomes with unique physico-chemical properties and subcellular localisation in the plasma membrane, nucleus, chloroplasts, and vacuole. Furthermore, we performed QPCR analysis of eight different antiporter genes after infiltrating the plants with 1 mM CySNO (S-nitroso-L-cysteine), a nitric oxide donor, in WT and the loss-of-function <i>atgsnor1-3</i> (disruptive S-nitrosoglutathione reductase 1 activity) plants. The <i>AT1G79400</i> (<i>CHX2</i>), <i>AT2G38170</i> (<i>RCI4</i>), and <i>AT5G17400</i> (<i>ER-ANT1</i>) showed a significant increase in their expression in response to CySNO infiltration. However, their expression in <i>atgsnor1-3</i> plants was found to be lower than in the WT plants, indicating a significant redundancy in the response of these genes to 1 mM levels of CySNO and physiological levels of SNOs in <i>atgsnor1-3</i>. On the other hand, a significant reduction in the expression of <i>AT1G16380</i> (<i>CHX1</i>), <i>AT2G47600</i> (<i>MHX1</i>), <i>AT3G13320</i> (<i>CAX2</i>), and <i>AT5G11800</i> (<i>KEA6</i>) was observed in WT plants after CySNO infiltration as well as in the leaves of <i>atgsnor1-3</i> plants. Our study identified three NO-responsive antiporter genes in <i>Arabidopsis</i>, indicating their roles in stress responsiveness and ion homeostasis that could be used for further validation of their roles in NO signalling in plants.