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Phosphorus (P) is an essential nutrient for plant growth and reproduction. Plants preferentially absorb P as orthophosphate (Pi), an ion that displays low solubility and that is readily fixed in the soil, making P limitation a condition common to many soils and Pi fertilization an inefficient practice. To cope with Pi limitation, plants have evolved a series of developmental and physiological responses, collectively known as the Pi starvation rescue system (PSR), aimed to improve Pi acquisition and use efficiency (PUE) and protect from Pi-starvation-induced stress. Intensive research has been carried out during the last 20 years to unravel the mechanisms underlying the control of the PSR in plants. Here we review the results of this research effort that have led to the identification and characterization of several core Pi starvation signaling components, including sensors, transcription factors, microRNAs (miRNAs) and miRNA inhibitors, kinases, phosphatases, and components of the proteostasis machinery. We also refer to recent results revealing the existence of intricate signaling interplays between Pi and other nutrients and antagonists, N, Fe, Zn, and As, that have changed the initial single-nutrient-centric view to a more integrated view of nutrient homeostasis. Finally, we discuss advances toward improving PUE and future research priorities., (Copyright © 2021 The Author. Published by Elsevier Inc. All rights reserved.)

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., (Copyright © 2017 Elsevier Ltd. All rights reserved.)