Protein kinase involved in salt tolerance and pH sensitivity, probably by regulating plasma membrane potential and cation influx. Positively controls the TRK1-TRK2 potassium transport system in response to potassium starvation. Stabilizes TRK1 in the plasma membrane by preventing its vacuolar sorting and degradation. Also stabilizes other plasma membrane nutrient transporters like CAN1, FUR4 and HXT1. May itself be subject to regulation by ARL1. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. NPR/HAL subfamily. HAL5 sub-subfamily.