Figure 1.

Overview of phosphate (Pi) transport in Arabidopsis plants. The transport route is shown in four parts: uptake from soil to roots, transport from roots to shoots, unloading in shoots and subcellular organelles, and transport to seeds in the form of phytic acid. The high-affinity Pi (PHT1) family (PHT1;1 and PHT1;4) of transporters plays a major role in Pi uptake from soil to roots. The PHO1 protein increases root-Pi xylem loading, whereas PHT1;5 plays a key role in the retranslocation of Pi from shoots to roots, and Pi mobilization to reproductive organs. In plant cell, vacuoles act as the primary intracellular compartments for Pi storage, and SPX-MFS1 and SPX-MFS3/PHT5;1 mediate vacuolar Pi influx and efflux, respectively. Furthermore, Pi is metabolized and transported from leaves to seeds in the form of phytic acid by the ABC-MRP-type phytic acid transporter. The levels of PHT1, PHO1 and PHO2 transporters are regulated by miR399 and cis-NAT_PHO1;2 in xylem, and by miR399 and IPS1/AT4 in roots. ABC-MRP, ATP binding cassette-multidrug resistance-associated protein; AT4, Arabidopsis thaliana 4; IPS1, induced by phosphate starvation 1; cis-NAT_PHO1;2, cis-natural antisense transcript phosphate transporter 1;2; PHT, high-affinity phosphate transporter; PHR1, phosphate starvation response 1; Pi, phosphate; PHO1, phosphate transporter 1; SPX-MFS3, SYG1/PHO81/XPR1 major facility superfamily 3; SPX-MFS1, SPX major facilitator superfamily 1; VPT1, vacuolar phosphate transporter 1.