SRA

Finite world rock phosphate (Pi) reserves will impose a major limitation on agricultural productivity and food security. Modern breeding programs are currently aimed at developing Pi-efficient crops having sustainable yields under reduced Pi fertilizer. In this regard, although the long-term response of plants to Pi stress is well documented, the early signaling events have yet to be elucidated. Here, we present studies showing that Pi, and the phytohormones, cytokinin and gibberellin function as root-to-shoot Pi stress signals that are perceived, in the shoot, by the vascular system. We further show that major changes occurred in the phloem mRNA population, and grafting studies revealed that thousands of mRNAs were delivered to specific sink tissues. Thus, the shoot vascular system acts as the site of root-derived Pi stress perception, and the phloem serves to deliver a cascade of signals to various sinks, presumably to coordinate Pi homeostasis at the whole-plant level.