PT  - JOURNAL ARTICLE
AU  - Jinsheng Zhu
AU  - Kelvin Lau
AU  - Robert K. Harmel
AU  - Robert Puschmann
AU  - Larissa Broger
AU  - Amit K. Dutta
AU  - Henning J. Jessen
AU  - Ludwig A. Hothorn
AU  - Dorothea Fiedler
AU  - Michael Hothorn
TI  - Two bifunctional inositol pyrophosphate kinases/phosphatases control plant phosphate homeostasis
AID  - 10.1101/467076
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 467076
4099  - http://biorxiv.org/content/early/2018/11/09/467076.short
4100  - http://biorxiv.org/content/early/2018/11/09/467076.full
AB  - Many eukaryotic proteins regulating phosphate (Pi) homeostasis contain SPX domains. We have previously shown that these domains act as cellular receptors for inositol pyrophosphate (PP-InsP) signaling molecules, suggesting that PP-InsPs may regulate Pi homeostasis. Here we report that simultaneous deletion of two diphosphoinositol pentakisphosphate kinases VIH1 and 2 in Arabidopsis impairs plant growth and leads to constitutive Pi starvation responses. We demonstrate that VIH1 and VIH2 are bifunctional cytosolic enzymes able to generate and break-down PP-InsPs. Point-mutants targeting the kinase and phosphatase active sites have opposing effects on plant Pi content and Pi starvation responses, while VIH1 and VIH2 protein levels remain constant in different Pi growth conditions. Enzymatic assays reveal that ATP-Mg2+ substrate levels can shift the relative kinase and phosphatase activities of full-length diphosphoinositol pentakisphosphate kinases. Deletion of phosphate starvation response transcription factors rescues vih1 vih2 mutant phenotypes, placing diphosphoinositol pentakisphosphate kinases and PP-InsPs in plant phosphate signal transduction cascades. We propose that VIH1 and VIH2 relay changes in cellular ATP concentration to changes in PPInsP levels, allowing plants to maintain cellular Pi concentrations constant and to trigger Pi starvation responses.