BRI1 is a critical component of a plasma-membrane receptor for plant steroids.
Most multicellular organisms use steroids as signalling molecules for physiological and developmental regulation. Two different modes of steroid action have been described in animal systems: the well-studied gene regulation response mediated by nuclear receptors, and the rapid non-genomic responses mediated by proposed membrane-bound receptors. Plant genomes do not seem to encode members of the nuclear receptor superfamily. However, a transmembrane receptor kinase, brassinosteroid-insensitive1 (BRI1), has been implicated in brassinosteroid responses. Here we show that BRI1 functions as a receptor of brassinolide, the most active brassinosteroid. The number of brassinolide-binding sites and the degree of response to brassinolide depend on the level of BRI1 protein. The brassinolide-binding activity co-immunoprecipitates with BRI1, and requires a functional BRI1 extracellular domain. Moreover, treatment of Arabidopsis seedlings with brassinolide induces autophosphorylation of BRI1, which, together with our binding studies, shows that BRI1 is a receptor kinase that transduces steroid signals across the plasma membrane.
Wang
Z Y
ZY
Howard Hughes Medical Institute and Plant Biology Laboratory, The Salk Institute for Biological Studies, 10010 N. Torrey Pines Road, La Jolla, California 92037, USA.
Seto
H
H
Fujioka
S
S
Yoshida
S
S
Chory
J
J
D017360:Arabidopsis; D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D002777:Cholestanols / Q000378:metabolism*; D004789:Enzyme Activation; D017343:Genes, Plant; D008024:Ligands; D009154:Mutation; D010766:Phosphorylation; D010840:Phytosterols / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011987:Receptors, Steroid / Q000378:metabolism*; D015398:Signal Transduction; D013260:Steroids, Heterocyclic / Q000378:metabolism*
D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D002777:Cholestanols; D008024:Ligands; D010840:Phytosterols; D011987:Receptors, Steroid; D013260:Steroids, Heterocyclic; D011494:Protein Kinases; C108270:BRI1 protein, Arabidopsis; C023623:brassinolide