Genome-wide identification of the HKT genes in five Rosaceae species and expression analysis of HKT genes in response to salt-stress in Fragaria vesca

Introduction: The high-affinity potassium transporter (HKT) gene family is implicated in the regulation of response to salt stress in different plants. Yet, knowledge remains very limited for them in the Rosaceae species. The whole genome sequences of the five Rosaceae species, including Fragaria vesca (woodland strawberry), Malus domestica (apple), Pyrus communis (pear), Prunus mume (mei) and Prunus persica (peach), give the opportunity to uncover the evolutionary pattern of the HKT genes among Rosaceae genomes. Objectives: The primary objective of this study was to identify the HKT genes in five Rosaceae species and understand the potential biological functions of the HKT genes in response to salt stress in Fragaria vesca. Methods: In this study, the HKT genes in five Rosaceae species were identified by bioinformatics. The phylogenetic tree was constructed and Ka and Ks values were calculated by MEGA 5.0. Genetic mapping of these genes were processed by MapInspect software. In addition, the physico-chemical properties, the cis-acting elements, the intron/exon structures, and the conserved domain motifs of these genes were analyzed and predicted by the websites of ProtParam, Pfam, PlantCARE, GSDS, MEME, and Motif Scan. Results: In the present study, a total of 12 HKT genes were identified from five Rosaceae species. In the phylogenetic tree, orthologous genes were clustering together rather than paralogous genes and PcHKTs underwent two species-specific duplications before the divergence of pear and apple.. Furthermore, various expression levels of FvHKT genes revealed that woodland strawberry HKT genes are associated in responding to the salt stress. The activities of ROS-scavenging enzymes, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were also measured in different treatments of salt-stressed woodland strawberry leaves, which suggested that the three enzymes may also take part in response to salt stress. Conclusion: The Ka/Ks ratio demonstrated that purifying selection played a major role in the evolutionary processes of HKT genes among the Rosaceae species, and FvHKT genes are involved in response to salt stress.