title: Intragenic suppression of a trafficking-defective brassinosteroid receptor mutant in Arabidopsis.
abstract: The cell surface receptor kinase BRASSINOSTEROID-INSENSITIVE-1 (BRI1) is the major receptor for steroid hormones in Arabidopsis. Plants homozygous for loss-of-function mutations in BRI1 display a reduction in the size of vegetative organs, resulting in dwarfism. The recessive bri1-5 mutation produces receptors that do not accumulate to wild-type levels and are retained mainly in the endoplasmic reticulum. We have isolated a dominant suppressor of the dwarf phenotype of bri1-5 plants. We show that this suppression is caused by a second-site mutation in BRI1, bri1-5R1. The bri1-5R1 mutation partially rescues the phenotypes of bri1-5 in many tissues and enhances bri1-5 phenotypes above wild-type levels in several other tissues. We demonstrate that the phenotypes of bri1-5R1 plants are due to both increased cell expansion and increased cell division. To test the mechanism of bri1-5 suppression, we assessed whether the phenotypic suppression in bri1-5R1 was dependent on ligand availability and the integrity of the signaling pathway. Our results indicate that the suppression of the dwarf phenotypes associated with bri1-5R1 requires both BR biosynthesis and the receptor kinase BRI1-ASSOCIATED KINASE-1 (BAK1). Finally, we show that bri1-5R1 partially restores the accumulation and plasma membrane localization of BRI1. Collectively, our results point toward a model in which bri1-R1 compensates for the protein-folding abnormalities caused by bri1-5, restoring accumulation of the receptor and its delivery to the cell surface.
authors.affiliation: Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA.
authors.forename: Youssef
authors.initials: Y
authors.lastname: Belkhadir
authors.forename: Amanda
authors.initials: A
authors.lastname: Durbak
authors.forename: Michael
authors.initials: M
authors.lastname: Wierzba
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Schmitz
authors.forename: Andrea
authors.initials: A
authors.lastname: Aguirre
authors.forename: Rene
authors.initials: R
authors.lastname: Michel
authors.forename: Scott
authors.initials: S
authors.lastname: Rowe
authors.forename: Shozo
authors.initials: S
authors.lastname: Fujioka
authors.forename: Frans E
authors.initials: FE
authors.lastname: Tax
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D060406:Brassinosteroids; D002455:Cell Division / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D002777:Cholestanols / Q000378:metabolism / Q000494:pharmacology; D004843:Epistasis, Genetic; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D011494:Protein Kinases / Q000235:genetics* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D036226:Seedlings / Q000166:cytology / Q000187:drug effects / Q000254:growth & development; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000187:drug effects; D013260:Steroids, Heterocyclic / Q000378:metabolism / Q000494:pharmacology; D056811:Unfolded Protein Response
chemical_list: D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D002777:Cholestanols; D013260:Steroids, Heterocyclic; D011494:Protein Kinases; C463660:BAK1 protein, Arabidopsis; C108270:BRI1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; C023623:brassinolide
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