Structural Features and Expression Regulation Analysis of Potassium Transporter Gene GmHAK5 in Soybean ( Glycine Max L.)

The HAK/KUP/KT potassium transporter gene family plays an important role in the uptake, transport, and distribution of potassium ions (K + ) in plants. To better understand the biological functions and expression regulation mechanism of potassium transporter gene GmHAK5 in soybean, the coding sequence (CDS) of GmHAK5 gene was cloned in this study, and its encoding protein had the typical structural features of the HAK/KUP/KT family genes. Phylogenetic analysis showed that all the plant HAK5 proteins were in Cluster I, in which GmHAK5 was closely related to PgrHAK5 of pomegranate ( Punica granatum ). The GmHAK5 protein was localized in the plasma membrane, which was consistent with its function as a potassium transporter involved in K + uptake. The GmHAK5 gene had a root-specific expression pattern, and was induced expression by low-potassium stress treatment. The GmHAK5 gene function was evaluated using a K + uptake-deficient yeast mutant R5421 (trk1Δ , trk2Δ ), and the transformation with GmHAK5 rescued the growth defect of mutant yeast strain R5421 at the low K + concentration range between 0 and 50 mM. Promoter sequence analysis demonstrated that the GmHAK5 promoter had five conserved root-specific expression motifs and an ARF2 binding site. Further dual-luciferase assays showed that ARF2 transcription factor in soybean ( GmARF2 ) can bind to the GmHAK5 promoter, and the luciferase (LUC) expression driven by the GmHAK5 promoter was relatively low when the GmARF2 gene was expressed, suggesting that GmARF2 might act as an inhibitor to participate in the transcriptional regulation of GmHAK5 gene in soybean. These results can provide a theoretical basis for further understanding the function and expression regulation mechanism of GmHAK5 , improving the potassium uptake efficiency and breeding varieties with high potassium efficiency in soybean.