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

Abstract

Apyrase (nucleotide triphosphate diphosphohydrolase, NTPDase; EC 3.6.1.5) functions in a variety of plant growth and developmental processes and responses to pathogens, in part, by regulating extracellular ATP (eATP) concentrations. In this study, we investigated possible roles for apyrase in the recruitment of phosphate (Pi) from extracellular nucleotides in Arabidopsis thaliana seedlings that constitutively express apyrase 1 (APY1). Under Pi limitation, both WT and APY1 seedlings had decreased Pi contents and a characteristic remodeling of root system architecture (RSA). This phosphate starvation response (PSR) was prevented by uptake of Pi released by metabolism of extracellular NTP, which supported normal seedling growth. In Pi-sufficient media, Pi contents of APY1 seedlings were higher than in WT seedlings. Addition of NTP reduced the number of LR and decreased Pi contents of WT seedlings but markedly increased both LR and root hair (RH) formation and Pi contents of APY1 seedlings. Genome-wide expression profiling revealed the repression of PSR genes in APY1 seedlings, relative to WT seedlings, consistent with their elevated Pi contents. The expanded RSA of APY1 seedlings was correlated with induction of >100 genes involved in regulation of auxin homeostasis, signaling and transport, which previous studies have shown to be increased when APY1 is overexpressed. APY1 regulation of [eNTP] and purinergic signaling may play a role in regulating this auxin response, resulting in enhanced uptake of Pi from the medium, including Pi released by eNTP metabolism.