Abstract
The CPA (cation proton antiporter) family plays an essential role during plant stress tolerance by regulating ionic and pH homeostasis of the cell. Radish fleshy roots are susceptible to abiotic stress during growth and development, especially salt stress. To date, CPA family genes have not yet been identified in radish and the biological functions remain unclear. In this study, 60 CPA candidate genes in radish were identified on the whole genome level, which were divided into three subfamilies including the Na+/H+ exchanger (NHX), K+ efflux antiporter (KEA), and cation/H+ exchanger (CHX) families. In total, 58 of the 60 RsCPA genes were localized to the nine chromosomes. RNA-seq. data showed that 60 RsCPA genes had various expression levels in the leaves, roots, cortex, cambium, and xylem at different development stages, as well as under different abiotic stresses. RT–qPCR analysis indicated that all nine RsNHXs genes showed up regulated trends after 250 mM NaCl exposure at 3, 6, 12, and 24h. The RsCPA31 (RsNHX1) gene, which might be the most important members of the RsNHX subfamily, exhibited obvious increased expression levels during 24h salt stress treatment. Heterologous over-and inhibited-expression of RsNHX1 in Arabidopsis showed that RsNHX1 had a positive function in salt tolerance. Furthermore, a turnip yellow mosaic virus (TYMV)-induced gene silence (VIGS) system was firstly used to functionally characterize the candidate gene in radish, which showed that plant with the silence of endogenous RsNHX1 was more susceptible to the salt stress. According to our results we provide insights into the complexity of the RsCPA gene family and a valuable resource to explore the potential functions of RsCPA genes in radish.
Highlights
Plants respond to salt stress by regulating the cell ion and pH balance through a variety of mechanisms, which are mainly dependent on ion transporters in cell membranes and organelle membranes [1,2]
Sci. 2020, 21, 8262 and complete RsCPA members were identified among the radish genome, which were correspondingly named as RsCPA01–RsCPA60 (Table S1)
These results indicated that RsNHX1 might play a positive role in the salt tolerance of radish
Summary
Plants respond to salt stress by regulating the cell ion and pH balance through a variety of mechanisms, which are mainly dependent on ion transporters in cell membranes and organelle membranes [1,2]. The CPA1 superfamily contains the Na+/H+ exchanger family (NHX), which is predicted to have 10–12 membrane-spanning domains in plants and it has been confirmed with an important effect on salt tolerance of plants [2,7]. In recent years, increasing evidence has indicated that some CPAs, especially NHXs, respond to salt stress, cell expansion, pH and ion balance regulation, osmotic regulation, and vesicle transport, as well as protein processing and floral organ development [15,16,17,18,19]. Some CPA genes have been proved to be related to salt stress response in other plant species, such as Arabidopsis, pear (Pyrus bretschneideri), grape (Vitis vinifera) and Helianthus tuberosus, the information of CPA genes identification at the whole genome level in radish is still limited [11,12,13,14]. The outcomes of our study lay the foundation for further characterization of these CPA genes for roles in radish salt-tolerance processes
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