title: Auxin signal transcription factor regulates expression of the brassinosteroid receptor gene in rice.
abstract: The phytohormones auxins and brassinosteroids are both essential regulators of physiological and developmental processes, and it has been suggested that they act inter-dependently and synergistically. In rice (Oryza sativa), auxin co-application improves the brassinosteroid response in the rice lamina inclination bioassay. Here, we showed that auxins stimulate brassinosteroid perception by regulating the level of brassinosteroid receptor. Auxin treatment increased expression of the rice brassinosteroid receptor gene OsBRI1. The promoter of OsBRI1 contains an auxin-response element (AuxRE) that is targeted by auxin-response factor (ARF) transcription factors. An AuxRE mutation abolished the induction of OsBRI1 expression by auxins, and OsBRI1 expression was down-regulated in an arf mutant. The AuxRE motif in the OsBRI1 promoter, and thus the transient up-regulation of OsBRI1 expression caused by treatment with indole-3-acetic acid, is essential for the indole-3-acetic acid-induced increase in sensitivity to brassinosteroids. These findings demonstrate that some ARFs control the degree of brassinosteroid perception required for normal growth and development in rice. Although multi-level interactions between auxins and brassinosteroids have previously been reported, our findings suggest a mechanism by which auxins control cellular sensitivity to brassinosteroids, and further support the notion that interactions between auxins and brassinosteroids are extensive and complex.
authors.affiliation: Ishikawa Prefectural University, Nonoichi, Ishikawa, 921-8836, Japan. sakamoto@ishikawa-pu.ac.jp
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Sakamoto
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Morinaka
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Inukai
authors.forename: Hidemi
authors.initials: H
authors.lastname: Kitano
authors.forename: Shozo
authors.initials: S
authors.lastname: Fujioka
mesh_terms: D060406:Brassinosteroids / Q000096:biosynthesis*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000494:pharmacology; D012275:Oryza / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000235:genetics / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D060406:Brassinosteroids; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; D014157:Transcription Factors; C030737:indoleacetic acid; C519615:BRI1 protein, Oryza sativa; D017346:Protein Serine-Threonine Kinases