Zm HAK5 and Zm HAK1 function in K~+ uptake and distribution in maize under low K~+ conditions

Potassium(K~+ ) is an essential macronutrient for plant growth and development. Transporters from the KT/HAK/KUP family play crucial roles in K~+ homeostasis and cell growth in various plant species. However, their physiological roles in maize are still unknown. In this study,we cloned ZmH AK5 and ZmH AK1 and investigated their functions in maize(Zea mays L.). In situ hybridization showed that Zm HAK5 was mainly expressed in roots,especially in the epidermis, cortex, and vascular bundle.ZmH AK5 was characterized as a high-affinity K~+ transporter.Loss of function of ZmH AK5 led to defective K~+ uptake in maize, under low K~+ conditions, whereas ZmH AK5-overexpressing plants showed increased K~+ uptake activity and improved growth. ZmH AK1 was upregulated under low K~+ stress, as revealed by RT-q PCR. ZmH AK1 mediated K~+ uptake when heterologously expressed in yeast, but its transport activity was weaker than that of ZmH AK5.Overexpression of Zm HAK1 in maize significantly affected K~+ distribution in shoots, leading to chlorosis in older leaves.These findings indicate that ZmH AK5 and ZmH AK1 play distinct roles in K~+ homeostasis in maize, functioning in K~+ uptake and K~+ distribution, respectively. Genetic manipulation of ZmH AK5 may represent a feasible way to improve K~+ utilization efficiency in maize.