Genome-wide identification of the cation/proton antiporter (CPA) gene family and functional characterization of the key member BnaA05.NHX2 in allotetraploid rapeseed

Rapeseed ( Brassica napus L.) is susceptible to nutrient stresses during growth and development. So far, the CPA ( cation proton antiporter ) family genes have not been identified in B. napus and their biological functions are still unclear. Integrated analyses were conducted to identify the molecular characteristics of rapeseed CPAs and their responses to nutrient stresses. Through bioinformatics analysis, 117 BnaCPAs were identified at the genome-wide level, and they were divided into three subfamilies: Na + /H + antiporter ( NHX ), K + efflux antiporter ( KEA ), and cation/H + antiporter ( CHX ). Transcriptomic profiling results showed that some BnaCPAs had various expression levels under different nutrient stresses especially under salt stress. Most members of the BnaNHX family showed a tendency of expression under different nutrient stress. The BnaNHX subfamily may be an important member of the BnaCPA family in regulating nutrient stress, especially in salt stress. We found that the salt tolerance of the transgenic overexpressed line constructed with BnaA05.NHX2 was significantly higher than that of the wild species Westar. Subcellular localization showed that BnaA05.NHX2 was localized on the tonoplast, and TEM combined with X-ray energy spectrum analysis revealed that the vacuolar Na + concentrations of the BnaA05.NHX2 -overexpressing rapeseed plants were significantly higher than those of wild type. According to our results, we provide insights into the complexity of the BnaCPA gene family and a valuable resource to explore the potential functions of BnaCPA genes in Brassica napus.