Novel signals in the regulation of Pi starvation responses in plants: facts and promises

•Inositol polyphosphates act as signals in phosphate homeostasis.•ROS signaling is associated to phosphate and iron control of root tip growth.•Thousands of RNAs in the plant transcriptome move among distant organs.•Mobile RNAs might act as systemic signals to control phosphate starvation responses and others.

Plants have evolved numerous adaptive developmental and metabolic responses to cope with growth in conditions of limited phosphate (Pi). Regulation of these Pi starvation responses (PSR) at the organism level involves not only cellular Pi perception in different organs, but also inter-organ communication of Pi levels via systemic signaling. Here we summarize recent discoveries on Pi starvation sensing and signaling, with special emphasis on structure-function studies that showed a role for inositol polyphosphates (InsP) as intracellular Pi signals, and on genomic studies that identified a large number of mRNAs with inter-organ mobility, which provide an immense source of potential systemic signals in the control of PSR and other responses.