Sensing and Signaling of Phosphate Starvation: From Local to Long Distance.

Phosphorus (P) is an essential nutrient, but low concentrations of phosphate (Pi), the predominant form in which it is acquired, in the soil often limits plant growth and reproduction. To adapt to low Pi availability, plants have developed intricate regulatory mechanisms that integrate the environmental stimuli with internal cues in order to exploit the use of P. These mechanisms include sensing external and internal Pi concentrations along with co-ordination between local and long-distance signaling pathways. The downstream actions governed by these signaling pathways include local responses for remodeling the root system architecture and systemic responses for modulating the activities of Pi uptake, remobilization and recycling. As an initially acquired molecule, Pi is considered to be a primary signal that directly regulates Pi starvation responses and sets in motion the generation of subsequent signals, such as hormones, sugars, P-containing metabolites, peptides and mobile RNAs. In this review, we summarize recent progress in understanding the regulatory pathways mediated by these signaling molecules that underlie both local and systemic responses to Pi deprivation, and discuss the potential cross-talk among these signaling pathways.