Role of Apyrase in Mobilization of Phosphate from Extracellular Nucleotides and in Regulating Phosphate Uptake in Arabidopsis

Apyrase (nucleotide triphosphate diphosphohydrolase, NTPDase; EC 3.6.1.5) functions in a variety of plant growth and developmental processes, as well as responses to pathogens, in part, by regulating extracellular ATP (eATP) concentrations. In this study, we investigated potential roles of apyrase in the recruitment of phosphate (Pi) from extracellular nucleotides in <i>Arabidopsis thaliana</i> seedlings that constitutively overexpress <i>apyrase 1</i> (<i>APY1</i>). Under Pi limitation, both WT and <i>APY1</i> seedlings had decreased Pi contents and a characteristic remodeling of root system architecture (RSA). This phosphate starvation response (PSR) was prevented by the uptake of Pi released through the metabolism of extracellular NTP, which occurred at a higher rate in <i>APY1</i> seedlings. <i>APY1</i> seedlings had higher Pi contents than WT seedlings on Pi-sufficient media supplemented with NTP and exhibited markedly increased LR and root hair (RH) formation. Genome-wide expression profiling revealed that this expanded RSA of <i>APY1</i> seedlings was correlated with the induction of >100 genes involved in regulation of auxin homeostasis, signaling, and transport, which previous studies have shown to be increased when <i>APY1</i> is overexpressed. APY1 regulation of [eNTP] and purinergic signaling may thus contribute to modulation of auxin responses, resulting in enhanced uptake of Pi from the medium, including Pi released via eNTP metabolism.