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Title: MOLECULAR MECHANISMS OF EARLY EVENTS IN BRASSINOSTEROID SIGNAL TRANSDUCTION.

Author
item WANG, XIAOFENG - N.C. STATE UNIVERISTY
item GOSHE, MICHAEL - N.C. STATE UNIVERSITY
item SODERBLOM, ERIK - N.C. STATE UNIVERSITY
item PHINNEY, BRETT - MICHIGAN STATE UNIVERSITY
item KUCHAR, JASON - MICHIGAN STATE UNIVERSITY
item LI, JIA - UNIVERSITY OF OKLAHOMA
item ASAMI, TADAO - RIKEN JAPAN
item YOSHIDA, SHIGEO - RIKEN JAPAN
item Huber, Steven
item CLOUSE, STEVEN - NORTH CAROLINA STATE

Submitted to: Plant Biology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/12/2005
Publication Date: 6/1/2005
Citation: Wang, X., Goshe, M.B., Soderblom, E.J., Phinney, B.S., Kuchar, J.A., Li, J., Asami, T., Yoshida, S., Huber, S.C., Clouse, S.D. 2005. Molecular mechanisms of early events in brassinosteroid signal transduction [abstract]. Plant Biology Annual Meeting. Available: http://abstracts/aspb.org/pb2005/public/P66/7861.html.

Interpretive Summary:

Technical Abstract: Brassinosteroids (BRs) regulate multiple aspects of plant growth and development and require an active BRASSINOSTEROID INSENSITIVE 1 (BRI1) and BRI1-ASSOCIATED RECEPTOR KINANSE 1 (BAK1) for hormone perception and signal transduction. Many animal receptor kinases exhibit ligand-dependent oligomerization followed by autophosphorylation and activation of the intracellular kinase domain. To determine if early events in BR signaling share this mechanism, we used co-immunoprecipitation of epitope-tagged proteins to show that <1>in vivo association of BRI1 and BAK1 was affected by endogenous and exogenous BR levels and that phosphorylation of both BRI1 and BAK1 on Thr residues was BR-dependent. Immunoprecipitation of epitope-tagged BRI1 from Arabidopsis plants followed by liquid chromatography-tandem mass spectrometry (LC/MS/MS), identified multiple BRI1 in vivo phosphorylation sites. We also identified four specific BAK1 autophosphorylation sites in vitro using LC/MS/MS. Site-directed mutagenesis of identified and predicted BRI1 phosphorylation sites revealed that two highly conserved activation loop residues were essential for kinase function in vitro. These findings are consistent with many aspects of the animal receptor kinase model in which ligand-dependent autophosphorylation of the activation loop generates a functional kinase, while phosphorylation of non-catalytic intracellular domains is required for recognition and/or phosphorylation of downstream substrates.