SPX1 is a Phosphate-dependent Inhibitor of Phosphate Starvation Response 1 in Arabidopsis

Overview

Journal Proc Natl Acad Sci U S A

Specialty Science

Date 2014 Oct 2

PMID 25271326

Citations 191

Authors

Maria Isabel Puga

Isabel Mateos

Rajulu Charukesi

Zhiye Wang

Jose M Franco-Zorrilla

Laura de Lorenzo

Maria L Irigoyen

Simona Masiero

Regla Bustos

Jose Rodriguez

Antonio Leyva

Vicente Rubio

Hans Sommer

Javier Paz-Ares

Affiliations

Soon will be listed here.

Abstract

To cope with growth in low-phosphate (Pi) soils, plants have evolved adaptive responses that involve both developmental and metabolic changes. Phosphate Starvation Response 1 (PHR1) and related transcription factors play a central role in the control of Pi starvation responses (PSRs). How Pi levels control PHR1 activity, and thus PSRs, remains to be elucidated. Here, we identify a direct Pi-dependent inhibitor of PHR1 in Arabidopsis, SPX1, a nuclear protein that shares the SPX domain with yeast Pi sensors and with several Pi starvation signaling proteins from plants. Double mutation of SPX1 and of a related gene, SPX2, resulted in molecular and physiological changes indicative of increased PHR1 activity in plants grown in Pi-sufficient conditions or after Pi refeeding of Pi-starved plants but had only a limited effect on PHR1 activity in Pi-starved plants. These data indicate that SPX1 and SPX2 have a cellular Pi-dependent inhibitory effect on PHR1. Coimmunoprecipitation assays showed that the SPX1/PHR1 interaction in planta is highly Pi-dependent. DNA-binding and pull-down assays with bacterially expressed, affinity-purified tagged SPX1 and ΔPHR1 proteins showed that SPX1 is a competitive inhibitor of PHR1 binding to its recognition sequence, and that its efficiency is highly dependent on the presence of Pi or phosphite, a nonmetabolizable Pi analog that can repress PSRs. The relative strength of the SPX1/PHR1 interaction is thus directly influenced by Pi, providing a link between Pi perception and signaling.

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