Identification and characterization of the strawberry KT/HAK/KUP transporter gene family in response to K+ deficiency

The potassium (K+) transporter/high-affinity K+/K(+)uptake transporters (KT/HAK/KUP), which contribute to K+ uptake, transport and allocation, take an indispensible part in ion homeostasis, as well as in plant adaptation to disadvantageous environmental stresses. However, molecular mechanisms in terms of K+ nutrition in fruit crops are still largely unknown. In this work, we isolated 15 KT/HAK/KUP transporter genes in strawberry (designated as FveKUP1 to FveKUP15), and checked their expression under both normal and K+ deficient conditions. Quantitative real-time PCR analyses indicated that most FveKUPs were largely expressed in flowers, with a responsive expression to K+ deficiency. Among these FveKUPs, FveKUP8 was the most abundantly expressed gene in all tested tissues, and its expression was significantly reduced by K+ deficiency. Further functional complementation experiment in bacterial mutant indicated that FveKUP8 can utilize external K+ under neutral proton environment, and might be a dominant K+ transporter during the flowering of strawberry plants. Our findings suggest that FveKUP8 is involved in K+ homeostasis in strawberry, and could be used as a potential gene for the molecular breeding of high K+ efficiency plants.