The SERK3 elongated allele defines a role for BIR ectodomains in brassinosteroid signalling

Nat Plants. 2018 Jun;4(6):345-351. doi: 10.1038/s41477-018-0150-9. Epub 2018 May 7.


The leucine-rich repeat receptor kinase (LRR-RK) BRASSINOSTEROID INSENSITIVE 1 (BRI1) requires a shape-complementary SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK) co-receptor for brassinosteroid sensing and receptor activation1. Interface mutations that weaken the interaction between receptor and co-receptor in vitro reduce brassinosteroid signalling responses2. The SERK3 elongated (elg) allele3-5 maps to the complex interface and shows enhanced brassinosteroid signalling, but surprisingly no tighter binding to the BRI1 ectodomain in vitro. Here, we report that rather than promoting the interaction with BRI1, the elg mutation disrupts the ability of the co-receptor to interact with the ectodomains of BRI1-ASSOCIATED-KINASE1 INTERACTING KINASE (BIR) receptor pseudokinases, negative regulators of LRR-RK signalling6. A conserved lateral surface patch in BIR LRR domains is required for targeting SERK co-receptors and the elg allele maps to the core of the complex interface in a 1.25 Å BIR3-SERK1 structure. Collectively, our structural, quantitative biochemical and genetic analyses suggest that brassinosteroid signalling complex formation is negatively regulated by BIR receptor ectodomains.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / metabolism*
  • Brassinosteroids / metabolism*
  • Membrane Proteins / metabolism*
  • Plant Proteins / metabolism
  • Protein Conformation
  • Protein Interaction Domains and Motifs
  • Protein Kinases / metabolism
  • Protein Serine-Threonine Kinases / metabolism*
  • Signal Transduction*
  • Structure-Activity Relationship


  • Arabidopsis Proteins
  • Brassinosteroids
  • Membrane Proteins
  • Plant Proteins
  • BIR2 protein, Arabidopsis
  • Protein Kinases
  • BAK1 protein, Arabidopsis
  • SERK protein, plant
  • Bir3 protein, Arabidopsis
  • Protein Serine-Threonine Kinases