The origin and evolution of HKT proteins with TrkH domain from aquatic plants to flowering plants

HKT proteins are the conserved voltage-gated ion channel proteins that act on the transmembrane transport of positive ions, but the evolutionary history of the HKT gene family is not clear. To create comparative HKT resources, we collected 134 HKT sequences in different phylogenetic lineages ranging from algae to angiosperms, encompassing fifty distinct taxonomic species. The evolutionary history of the HKT gene family was revisited through phylogenetic reconstruction. Phylogenetic reconstruction and comparative genomic analysis suggested that the HKT gene family originated from land plants and had a large number of tandem duplications. The evolution of HKT genes was mostly linear in non-seed plants. The genome duplication event was a potential factor in the change of the HKT gene copies in seed plants. In eudicots, the contraction event of HKT genes occurred every time the plant underwent a whole-genome duplication event after the ancient triplication. Amino acid sequence variations in the HKT transporters of TrkH domain influence their tertiary protein structure. Meanwhile, six HKT genes, represented by the Vitis vinifera, exhibit tissue-specific expression patterns and respond differentially to salt and drought stress. Frequent gene and genome duplications contributed significantly to the expansion/contraction of the HKT gene family. Our findings regarding the origin and evolution of HKT offer unique backgrounds and new insight into the functional evolution of this gene family.