Transcriptional regulation and functional properties of Arabidopsis Pht1;4, a high affinity transporter contributing greatly to phosphate uptake in phosphate deprived plants

Phosphate mobilization into the plant is a complex process requiring numerous transporters for absorption and translocation of this major nutrient. In the genome of Arabidopsis thaliana, nine closely related high affinity phosphate transporters have been identified but their specific roles remain unclear. Here we report the molecular, histological and physiological characterization of Arabidopsis pht1;4 high affinity phosphate transporter mutants. Using GUS-gene trap and in situ hybridization, Pht1;4 was found mainly expressed in inorganic phosphate (Pi) limiting medium in roots, primarily in the epidermis, the cortex and the root cap. In addition to this, expression was also observed at the lateral root branch points on the primary root and in the stele of lateral roots, suggesting a role of Phi 1;4 in phosphate absorption and translocation. from the growth medium to the different parts of the plant. Pi-starved pht1;4 plantlets exhibited a strong reduction of phosphate uptake capacity (40%). This phenotype appears only related to the pht1,-4 mutation as there were no obvious changes in the expression of other Pht1 family members in the mutants background. However, after 10 days of growth on phosphate deficient or sufficient medium, the Pi content in the mutants was not significantly different from that of the corresponding wild type controls. Furthermore, the mutants did not display any obvious growth defects or visible phenotypes when grown on a low phosphate containing medium. The work described here offers a first step in the complex genetic dissection of the phosphate transport system in planta.