Metal transporter encoding gene families in Fabaceae: II. Cation/H+ exchanger (CAX) encoding genes

Abstract

The plant CAtion/H⁺ eXchangers (CAX) proteins belong to Ca²⁺/cation antiporter (CaCA) superfamily. By using in silico methods, the CAX encoding genes in the genome of six legume species have been identified in this work. In examined legume genomes, the CAX genes belong to a small multigenic family. The number of the CAX genes in these legume species is 17 (soybean), 6 (common bean and C. cajan), 5 (M. truncatula and C. arietinum) and 3 genes (L. japonicus), respectively. The legume CAX genes vary in genomic full-length ranging from 1,213 to 11,561 base pairs. All of the genes exhibit introns (from 4 to 11 introns). Their deduced full-length protein sequences range from 248 to 718 amino acids. Theoretical pI values of most (39/42) of legume CAX proteins were less than 7. The secondary structure modelling of protein exhibit transmembrane helix region (from 3 to 11 regions). Half of all (23/42) included 11 transmembrane helix regions. Based on phylogeny analysis, all of the legume CAX were divided into two groups, A and B, each consisting of two subgroups. The phylogeny suggested an ancient gene duplication in the genome of legumes ancestry. The recent gene duplication even was only detected in the soybean genome after the speciation. The expression analysis showed that all of 3 L. japonicus CAX genes expressed in all examined tissues. However, the expression of C. cajan CAX genes was not detected. For each of 4 remaining legumes, the CAX genes were differed in their expression level depending on studied tissues. The tissue-specific expressions of some CAX genes were observed in 5 out of the 6 legume species, except C. cajan.