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

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 the length of both lateral roots and root hairs,while OsHAK5 overexpression increased PAT,tiller number,and root hair length,irrespective of the 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 included the OsHAK5-mediated decrease of transmembrane potential(depolarization),increase of extracellular pH,and increase 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 ATP-dependent auxin transport.Both functions may underlie the prominent effect of OsHAK5 on rice architecture,which may be exploited in the future to increase crop yield via genetic manipulations.