The Pht1 ;9 and Pht1 ;8 transporters mediate inorganic phosphate acquisition by the Arabidopsis thaiiana root during phosphorus starvation

摘要

The activation of high-affinity root transport systems is the best-conserved strategy employed by plants to cope with low inorganic phosphate (Pi) availability, a role traditionally assigned to Pi transporters of the Pht1 family, whose respective contributions to Pi acquisition remain unclear. To characterize the Arabidopsis thaiiana Pht1 ;9 transporter, we combined heterologous functional expression in yeast with expression/subcellular localization studies and reverse genetics approaches in planta.Double Pht1;9/Pht1;8 silencing lines were also generated to gain insight into the role of the closest Pht1 ;9 homolog. Pht1;9 encodes a functional plasma membrane-localized transporter that mediates high-affinily Pi/H! symport activity in yeast and is highly induced in Pi-starved Arabidopsis roots. Null pht1;9 alleles exhibit exacerbated responses to prolonged Pi limitation and enhanced tolerance to arsenate exposure, whereas Pht1;9 overexpression induces the opposite phenotypes. Strikingly, Pht1;9/Pht1;8 silencing lines display more pronounced defects than the pht1;9 mutants. Pi and arsenic plant content analyses confirmed a role of Pht1;9 in Pi acquisition during Pi starvation and arsenate uptake at the root-soil interface. Although not affecting plant internal Pi repartition, Pht1;9 activity influences the overall Arabidopsis Pi status. Finally, our results indicate that both the Pht1 ;9 and Pht1 ;8 transporters function in sustaining plant Pi supply on environmental Pi depletion.