title: OCTOPUS Negatively Regulates BIN2 to Control Phloem Differentiation in Arabidopsis thaliana.
abstract: The phloem is a vascular strand that conducts photoassimilates and systemic signals throughout the plant to coordinate growth. To date, few molecular genetic determinants have been identified to control both specification and differentiation of this tissue [1-3]. Among them, OCTOPUS (OPS) protein was previously identified as a polarly localized plasma membrane-associated protein of unknown biochemical function whose broad provascular expression becomes restricted to the phloem upon differentiation [2]. OPS loss-of-function mutants showed an altered vascular network in cotyledons and an intermittent phloem differentiation in the root [2, 4]. Here, we demonstrate a role for OPS as a positive regulator of the brassinosteroid (BR) signaling pathway. Indeed, transgenic lines overexpressing OPS (OPS-OE) display the hallmarks of constitutively overactivated BR mutants. Physiological and genetic analyses place OPS as a positive regulator of the BR signaling pathway upstream of the key transcription factors BES1 and BZR1. Directed protein interactions with known BR signaling proteins identified BIN2, a GSK3 protein involved in multiple signaling pathways, as a partner of OPS. This interaction recruits BIN2 to the plasma membrane, thus preventing its inhibitory activity in the nucleus. Finally, both bikinin (a potent inhibitor of GSK3 [5]) treatment and downstream dominant mutants bes1-D [6] and bzr1-D [7] can rescue phloem defects of ops in the root. Together, our data show that OPS antagonizes BIN2 to promote phloem differentiation.
authors.affiliation: INRA, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, 78026 Versailles, France; AgroParisTech, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, 78026 Versailles, France; Université Paris-Sud, 91405 Orsay Cedex, France.
authors.forename: Pauline
authors.initials: P
authors.lastname: Anne
authors.affiliation: INRA, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, 78026 Versailles, France; AgroParisTech, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, 78026 Versailles, France.
authors.forename: Marianne
authors.initials: M
authors.lastname: Azzopardi
authors.affiliation: INRA, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, 78026 Versailles, France; AgroParisTech, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, 78026 Versailles, France.
authors.forename: Lionel
authors.initials: L
authors.lastname: Gissot
authors.affiliation: INRA, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, 78026 Versailles, France; AgroParisTech, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, 78026 Versailles, France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Beaubiat
authors.affiliation: INRA, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, 78026 Versailles, France; AgroParisTech, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, 78026 Versailles, France. Electronic address: kian.hematy@versailles.inra.fr.
authors.forename: Kian
authors.initials: K
authors.lastname: Hématy
authors.affiliation: INRA, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, 78026 Versailles, France; AgroParisTech, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, 78026 Versailles, France. Electronic address: palauqui@versailles.inra.fr.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Palauqui
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D060406:Brassinosteroids / Q000378:metabolism; D002478:Cells, Cultured; D018548:Cotyledon / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D009154:Mutation; D052585:Phloem / Q000254:growth & development / Q000378:metabolism; D010766:Phosphorylation; D018517:Plant Roots / Q000378:metabolism; D030821:Plants, Genetically Modified; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D008565:Membrane Proteins; D011494:Protein Kinases; C571839:OCTOPUS protein, Arabidopsis; C448985:At4g18710 protein, Arabidopsis