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Expression of a Na+/H+ antiporter RtNHX1 from a recretohalophyte Reaumuria trigyna improved salt tolerance of transgenic Arabidopsis thaliana

Li, Ningning, Wang, Xue, Ma, Binjie, Du, Chao, Zheng, Linlin, Wang, Yingchun
Journal of plant physiology 2017 v.218 pp. 109-120
Arabidopsis thaliana, abscisic acid, acid treatment, antioxidants, biomass production, biosynthesis, catalase, chlorophyll, enzyme activity, gene expression regulation, gene overexpression, genes, homeostasis, leaves, mutants, open reading frames, peroxidase, potassium, proline, root growth, salt stress, salt tolerance, seed germination, shrubs, sodium, sodium chloride, sodium-hydrogen antiporter, transcriptome, transgenic plants, vacuoles, yeasts
Reaumuria trigyna is an endangered recretohalophyte and a small xeric shrub that is endemic to the eastern Alxa and western Ordos areas of Inner Mongolia, China. Using transcriptome data, we identified a 1662-bp open reading frame encoding a 553-amino-acid protein corresponding to a Na+/H+ antiporter (RtNHX1) from R. trigyna. RtNHX1 was rapidly up-regulated by NaCl and exogenous abscisic acid treatment and had different tissue-specific expression patterns before and after salt-stress treatment. Overexpression of RtNHX1 enhanced seed germination, biomass accumulation, chlorophyll content, and root elongation in transgenic Arabidopsis plants under salt stress and rescued the salt-sensitive deficiencies of the nhx1 mutant. POD and CAT enzyme activities, proline content, and RWC all increased significantly in salt-stressed transgenic Arabidopsis plants, whereas MDA content did not. Additionally, there was a corresponding upregulation of some antioxidant-enzyme, proline biosynthesis and other stress responsive genes (AtPOD1, AtCAT1, AtP5CS1, AtP5CS2, AtRD29A, AtRD29B, AtKIN1, and AtABI2). The transgenic Arabidopsis plants accumulated more K+ and less Na+ in their leaves and had lower Na+/K+ ratios than WT plants. This was reflected in the upregulation of some ion transport-related genes (AtAVP1, AtSOS1, AtKUP6, and AtKUP8). When RtNHX1 was expressed in the AXT3 yeast strain, the accumulation of Na+ and K+ in the vacuole increased and the Na+/K+ ratio decreased. These results reveal that R. trigyna RtNHX1 is a functional antiporter that sequesters Na+ and K+ in the vacuole and could confer salt tolerance on transgenic Arabidopsis plants by maintaining Na+/K+ homeostasis and enhancing osmotic and antioxidant regulatory capacity. These results suggest that RtNHX1 may be a good target for improving salt tolerance in plants.