title: Deactivation of the Arabidopsis BRASSINOSTEROID INSENSITIVE 1 (BRI1) receptor kinase by autophosphorylation within the glycine-rich loop.
abstract: The activity of the dual-specificity receptor kinase, brassinosteroid insensitive 1 (BRI1), reflects the balance between phosphorylation-dependent activation and several potential mechanisms for deactivation of the receptor. In the present report, we elucidate a unique mechanism for deactivation that involves autophosphorylation of serine-891 in the ATP-binding domain. Serine-891 was identified previously as a potential site of autophosphorylation by mass spectrometry, and sequence-specific antibodies and mutagenesis studies now unambiguously establish phosphorylation of this residue. In vivo, phosphorylation of serine-891 increased slowly with time following application of brassinolide (BL) to Arabidopsis seedlings, whereas phosphorylation of threonine residues increased rapidly and then remained constant. Transgenic plants expressing the BRI1(S891A)-Flag-directed mutant have increased hypocotyl and petiole lengths, relative to wild-type BRI1-Flag (both in the bri1-5 background), and accumulate higher levels of the unphosphorylated form of the BES1 transcription factor in response to exogenous BL. In contrast, plants expressing the phosphomimetic S891D-directed mutant are severely dwarfed and do not accumulate unphosphorylated BES1 in response to BL. Collectively, these results suggest that autophosphorylation of serine-891 is one of the deactivation mechanisms that inhibit BRI1 activity and BR signaling in vivo. Many arginine-aspartate (RD)-type leucine-rich repeat receptor-like kinases have a phosphorylatable residue within the ATP-binding domain, suggesting that this mechanism may play a broad role in receptor kinase deactivation.
authors.affiliation: Department of Agriculture, University of Illinois, Urbana, IL 61801, USA.
authors.forename: Man-Ho
authors.initials: MH
authors.lastname: Oh
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Wang
authors.forename: Steven D
authors.initials: SD
authors.lastname: Clouse
authors.forename: Steven C
authors.initials: SC
authors.lastname: Huber
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism*; D060406:Brassinosteroids; D004789:Enzyme Activation; D005998:Glycine / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D030821:Plants, Genetically Modified; D011494:Protein Kinases / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D013329:Structure-Activity Relationship
chemical_list: D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D011993:Recombinant Fusion Proteins; D010768:Phosphoserine; D011494:Protein Kinases; C108270:BRI1 protein, Arabidopsis; D005998:Glycine