Graduate Student North Carolina State University Raleigh, North Carolina
Body of Abstract: Phosphate (Pi) is a critical macronutrient required for normal plant growth and development. Plants have evolved several strategies to grow in phosphate limited soils including the activation of phosphate starvation responsive (PSR) genes which results in increased Pi uptake from soil, and altered Pi scavenging and recycling from existing stores. The control of these adaptations however is not fully understood. Inositol phosphates (InsPs) are synthesized by the sequential phosphorylation of a six carbon myo-inositol precursor. The fully phosphorylated form, inositol hexakisphosphate (InsP6) serves as a major store of phosphate. InsP6 can be further pyro-phosphorylated by IPTK1 and VIP kinases to form inositol pyrophosphates (InsP7 and InsP8) which have emerged as important regulators of eukaryotic responses to phosphate starvation via interaction with SPX regulatory proteins. Arabidopsis contains two highly conserved VIP enzymes AtVIP1 and AtVIP2. We generated double Atvip1/Atvip2 mutants and characterized their response to low phosphate. The vip mutants exhibit altered responses to phosphate starvation compared to wild type plants. Additionally, a subset of PSR genes are basally downregulated in the vip mutants; however most PSR genes remain inducible under low phosphate conditions, suggesting the presence of redundant regulatory systems. Together, these data indicate a complex regulation of phosphate homeostasis by InsP8 / SPX interaction.