Phosphate scouting by root tips

- The two most abundant metals in soil, Fe and Al, limit phosphate bioavailability.
- Root tips sense phosphate together with Fe to locally inform root development.
- Low phosphate rapidly inhibits root cell elongation and, with delay, cell division.
- STOP1-ALMT1 and PDR2-LPR1 action mediate responses of root tips to low phosphate.
- Antagonistic interactions between phosphate, Fe and Al converge in phosphate sensing.

Chemistry assigns phosphate (Pi) dominant roles in metabolism; however, it also renders the macronutrient a genuinely limiting factor of plant productivity. Pi bioavailability is restricted by low Pi mobility in soil and antagonized by metallic toxicities, which force roots to actively seek and selectively acquire the vital element. During the past few years, a first conceptual outline has emerged of the sensory mechanisms at root tips, which monitor external Pi and transmit the edaphic cue to inform root development. This review highlights new aspects of the Pi acquisition strategy of Arabidopsis roots, as well as a framework of local Pi sensing in the context of antagonistic interactions between Pi and its major associated metallic cations, Fe3+ and Al3+.