Genome-Wide Identification and Functional Characterization of the Cation Proton Antiporter (CPA) Family Related to Salt Stress Response in Radish ( L.).

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, family genes have not yet been identified in radish and the biological functions remain unclear. In this study, 60 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 genes were localized to the nine chromosomes. RNA-seq. data showed that 60 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 genes showed up regulated trends after 250 mM NaCl exposure at 3, 6, 12, and 24h. The 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 in showed that 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 was more susceptible to the salt stress. According to our results we provide insights into the complexity of the gene family and a valuable resource to explore the potential functions of genes in radish.