Brassinosteroid-insensitive-1 is a ubiquitously expressed leucine-rich repeat receptor serine/threonine kinase.
Brassinosteroid (BR) mutants of Arabidopsis have pleiotropic phenotypes and provide evidence that BRs function throughout the life of the plant from seedling development to senescence. Screens for BR signaling mutants identified one locus, BRI1, which encodes a protein with homology to leucine-rich repeat receptor serine (Ser)/threonine (Thr) kinases. Twenty-seven alleles of this putative BR receptor have been isolated to date, and we present here the identification of the molecular lesions of 14 recessive alleles that represent five new mutations. BR-insensitive-1 (BRI1) is expressed at high levels in the meristem, root, shoot, and hypocotyl of seedlings and at lower levels later in development. Confocal microscopy analysis of full-length BRI1 fused to green fluorescent protein indicates that BRI1 is localized in the plasma membrane, and an in vitro kinase assay indicates that BRI1 is a functional Ser/Thr kinase. Among the bri1 mutants identified are mutants in the kinase domain, and we demonstrate that one of these mutations severely impairs BRI1 kinase activity. Therefore, we conclude that BRI1 is a ubiquitously expressed leucine-rich repeat receptor that plays a role in BR signaling through Ser/Thr phosphorylation.
Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA.
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DM
Friedrichsen
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CA
Joazeiro
J
J
Li
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Hunter
J
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Chory
D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins; D007930:Leucine / Q000235:genetics*; D008164:Luminescent Proteins / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D015398:Signal Transduction
D029681:Arabidopsis Proteins; D008164:Luminescent Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D011494:Protein Kinases; C108270:BRI1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; D007930:Leucine