Attenuated down-regulation of PHOSPHATE TRANSPORTER1 genes as a mechanism for phosphorus sensitivity in phosphorus-efficient Hakea prostrata (Proteaceae)

Background and aims Phosphorus (P) is an essential plant nutrient and integral for crop yield. However, plants adapted to P-impoverished environments, such as Hakea prostrata (Proteaceae), are often sensitive to P supplies that would be beneficial to other plants. The strategies for phosphate uptake and transport in P-sensitive species have received little attention. Methods Using a recently-assembled transcriptome of H. prostrata , we identified 10 putative members of the PHOSPHATE TRANSPORTER1 ( PHT1 ) gene family, which is responsible for inorganic phosphate (Pi) uptake and transport in plants. We examined plant growth, organ P concentrations and the transcript levels for the eight PHT1 members that were expressed in roots of H. prostrata at Pi supplies ranging from P-impoverished to P-excess. Key results Hakea prostrata plants suppressed cluster root growth above ecologically-relevant Pi supplies, whilst non-cluster root mass ratios were constant. Root P concentrations increased with increasing Pi supply. Of the eight H. prostrata PHT1 genes tested, four had relatively high transcript amounts in young roots suggesting important roles in Pi uptake; however, a maximum five-fold difference in expression between P-impoverished and P-excess conditions indicated a low P-responsiveness for these genes. The HpPHT1;8 and HpPHT1;9 genes were paralogous to Pi-responsive Arabidopsis thaliana PHT1;8 and PHT1;9 orthologues involved in root-to-shoot translocation of P, but only HpPHT1;9 was P responsive. Conclusions An attenuated ability of H. prostrata to regulate PHT1 expression in response to Pi supply is likely responsible for its low capacity to control P uptake and contributes to its high P sensitivity.