Abstract

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.