title: SPX1 is a phosphate-dependent inhibitor of Phosphate Starvation Response 1 in Arabidopsis.
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.
authors.affiliation: Departments of Plant Molecular Genetics and.
authors.forename: María Isabel
authors.initials: MI
authors.lastname: Puga
authors.affiliation: Departments of Plant Molecular Genetics and.
authors.forename: Isabel
authors.initials: I
authors.lastname: Mateos
authors.affiliation: Departments of Plant Molecular Genetics and.
authors.forename: Rajulu
authors.initials: R
authors.lastname: Charukesi
authors.affiliation: State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou 310058, China; and.
authors.forename: Zhiye
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Genomics Unit, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Cientificas, 28049 Madrid, Spain;
authors.forename: José M
authors.initials: JM
authors.lastname: Franco-Zorrilla
authors.affiliation: Departments of Plant Molecular Genetics and.
authors.forename: Laura
authors.initials: L
authors.lastname: de Lorenzo
authors.affiliation: Departments of Plant Molecular Genetics and.
authors.forename: María L
authors.initials: ML
authors.lastname: Irigoyen
authors.affiliation: Department of Plant Molecular Genetics, Max-Planck-Institut für Züchtungsforschung, 50829 Cologne, Germany.
authors.forename: Simona
authors.initials: S
authors.lastname: Masiero
authors.affiliation: Departments of Plant Molecular Genetics and.
authors.forename: Regla
authors.initials: R
authors.lastname: Bustos
authors.affiliation: Cellular and Molecular Biology, and.
authors.forename: José
authors.initials: J
authors.lastname: Rodríguez
authors.affiliation: Departments of Plant Molecular Genetics and.
authors.forename: Antonio
authors.initials: A
authors.lastname: Leyva
authors.affiliation: Departments of Plant Molecular Genetics and.
authors.forename: Vicente
authors.initials: V
authors.lastname: Rubio
authors.affiliation: Department of Plant Molecular Genetics, Max-Planck-Institut für Züchtungsforschung, 50829 Cologne, Germany.
authors.forename: Hans
authors.initials: H
authors.lastname: Sommer
authors.affiliation: Departments of Plant Molecular Genetics and jpazares@cnb.csic.es.
authors.forename: Javier
authors.initials: J
authors.lastname: Paz-Ares
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018744:DNA, Plant / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010710:Phosphates / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D018744:DNA, Plant; D009687:Nuclear Proteins; C514695:PHR1 protein, Arabidopsis; D010710:Phosphates; C000597306:SPX1 protein, Arabidopsis; D014157:Transcription Factors
keywords: phosphate sensor; phosphate starvation signaling