The Potassium Transporter OsHAK5 Alters Rice Architecture via ATP-Dependent Transmembrane Auxin Fluxes

Abstract Plant HAK/KUP/KT family members function as plasma membrane (PM) H+-K+ symporters and may modulate chemiosmotically driven polar auxin transport (PAT). Here, we show that inactivation of OsHAK5, a rice K+ transporter gene, decreased rootward and shootward PAT, tiller number and length of both lateral roots and root hairs, while OsHAK5-overexpression increased PAT, root hair and tiller number irrespective of K+ supply. Inhibitors of ATP-binding-cassette type-B transporters, NPA and BUM, abolished the OsHAK5-overexpression effect on PAT. The mechanistic basis of these changes includes OsHAK5 decrease of transmembrane potential (depolarization), increase of extracellular pH, and enhancement of PM-ATPase activity. These findings highlight the dual roles of OsHAK5 in altering cellular chemiosmotic gradients (generated continuously by PM H+-ATPase) and regulating an ATP-dependent auxin transport. Both functions may underlie the prominent effect of OsHAK5 on rice architecture. This regulation is likely to be exploited in future manipulations to increase crop yield in the field.