Long-distance call from phosphate: systemic regulation of phosphate starvation responses

Phosphate (P-i) is an essential nutrient for plants but is normally fixed in soil, which limits plant growth and reproduction. In response to low availability of P-i, shoots and roots react differently but cooperatively to improve P-i acquisition from the rhizosphere and adjust P-i distribution and metabolism within plants. Shoot and root responses are coordinated by the trafficking of various kinds of systemic signals through the vasculature. Mutual communication between different tissues is necessary to integrate the environmental stimuli with the internal cues at the whole-plant level. Different approaches have been used to monitor or manipulate components in the vascular stream to reveal several candidates of systemic signals from roots or shoots, including photosynthates, phytohormones, microRNAs, and P-i. In addition, the downstream signalling pathways mediated by these signals have been discovered. The crosstalk among different signalling pathways has been revealed, showing the complexity of the P-i signalling network. In this review, we summarize the approaches used for studying systemic signalling and discuss recent progress and challenges in investigating the systemic signalling pathway that integrates P-i starvation responses to maintain P-i at physiological concentrations. Knowledge gained from this study may help improve the phosphorus use efficiency of crops.