Cloning and functional analysis of PbHAK17 from Pyrus betulifolia in response to low potassium and salt stress

Objectives Pyrus betulifolia is a commonly cultivated rootstock with high salt tolerance. A potassium transporter gene, PbHAK17 that was screened out from Pyrus betulaefolia, seems respond to both K and salt stress. We studied its expression and function characteristics through bioinformatics, gene expression, and genetic transformation analysis.

Methods Firstly, the PbHAK17 gene was cloned, and the protein structure and phylogenetic relationship were analyzed. Subcellular localization, K-deficient yeast, and transgenic Arabidopsis thaliana experiments were then employed to determine the function of the gene. The growth status, K⁺ and Na⁺ contents of overexpressed Arabidopsis lines and wild-type Arabidopsis lines were analyzed under K deficiency and normal K level (0 and 3 mmol/L K⁺), and normal condition and salt stress (50 and 200 mmol/L Na⁺).

Results The PbHAK17 is 2370 bp in length and encodes 789 amino acids, and the PbHAK17 protein was localized on the cell membrane. K deficiency and salt stress induced a significant up-expression of PbHAK17 in the root of Pyrus betulifoliaand. In conditions of potassium deficiency, the PbHAK17 yeast transformant showed significant promotion effect on the growth of deficient yeast through supplementing K, and restored the growth of deficient yeast under salt stress. The K⁺ content in leaves and roots of Arabidopsis overexpressing PbHAK17 was higher than that of wild-type Arabidopsis under low K treatment. Under the same Na⁺ concentration, PbHAK17 transgenic Arabidopsis had larger and denser leaves than wild-type Arabidopsis, and the K⁺/Na⁺ ratio of roots was significantly higher than that of wild-type Arabidopsis.

Conclusions The pear potassium transporter gene PbHAK17 was localized in the plasma membrane of the cell, K deficiency and salt stress could induce the overexpression of PbHAK17 in the root system, increase K⁺ accumulation in root and leaves, and regulate the K⁺/Na⁺ ratio in plant, bring about stronger tolerance of Pyrus betulifolia to K deficiency and salt stress.