Potassium transporters and their evolution in plants under salt stress

The global crop production areas have been affected by soil salinity, mainly due to salt stress-induced restriction of plant growth and crop productivity. The increasing number of studies revealed that potassium transporters play a key role in plant salt tolerance in the last few decades. In this chapter, we summarize the molecular and evolutionary aspects of the main potassium transport systems, including the Shaker-type K+ channels (AKT/KAT/GORK/SKOR), high-affinity K+ transporters (HAKs), high-affinity Na+:K+ transporters (HKTs), Na+/H+ antiporters (NHXs), and vacuolar two-pore K+ channels (TPKs) in plant and their evolution. We also discuss the mechanisms of K+ uptake in salt-stressed plants: K+ absorption from the saline soil, xylem K+ loading and unloading, phloem K+ recirculation, and replenishing cytosolic K+ from the vacuolar pool. Moreover, we review the efflux mechanism of outward K+ channels (GORK)-mediated and nicotinamide adenine dinucleotide phosphate oxidase-dependent reactive oxygen species-triggered K+ efflux in salt-stressed plants. In summary, we suggest that the manipulation of both K+ uptake and efflux systems using genome editing technology should be focused to breed robust salt-tolerant crops to meet the increasing global food demand