Positive Regulatory Roles of HAK5 under K Deficiency or High Salt Stress.

HAK/KUP/KT family members have been identified as playing key roles in K uptake and salt tolerance in numerous higher plants. However, their functions in cassava ( Cantz) remain unknown. In this study, a gene encoding for a high-affinity potassium transporter () was isolated from cassava and its function was investigated. Subcellular localization analysis showed that HAK5 is a plasma membrane-localized transporter. RT-PCR and RT-qPCR indicated that is predominantly expressed in cassava roots, where it is upregulated by low potassium or high salt; in particular, its highest expression levels separately increased by 2.2 and 2.9 times after 50 µM KCl and 150 mM NaCl treatments. When heterologously expressed in yeast, HAK5 mediated K uptake within the cells of the yeast strain CY162 and rescued the salt-sensitive phenotype of AXT3K yeast. overexpression in transgenic plants exhibited improved growth and increased shoot K content under low potassium conditions. Under salt stress, transgenic plants accumulated more K in the shoots and roots and had reduced Na content in the shoots. As a result, transgenic demonstrated a more salt-tolerant phenotype. These results suggest that HAK5 functions as a high-affinity K transporter under K starvation conditions, improving K/Na homeostasis and thereby functioning as a positive regulator of salt stress tolerance in transgenic . Therefore, HAK5 may be a suitable candidate gene for improving K utilization efficiency and salt tolerance.