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<p>Brassinosteroids (BRs) are chemically diverse plant steroid hormones produced via a branched biosynthetic pathway. The potent BR brassinolide is sensed by the membrane receptor kinase BRI1 and a SERK co-receptor, but the physiological functions of other abundant BRs remain to be characterized. Here we present quantitative binding kinetics for 4 <i>Arabidopsis thaliana</i> BR receptors and 15 BRs, which define the key chemical features required for high-affinity receptor binding, ligand positioning and co-receptor recognition. BRI1, BRL1 and BRL3 share overlapping ligand preferences, whereas BRL2 binds C<sub>28</sub> BRs with moderate affinity. Structural analyses of BR-bound BRI1 and BRL3 ectodomains combined with extensive in vitro and in vivo mutagenesis studies reveal a high structural plasticity of the hormone-binding pocket. Functional assays using structure-based BR agonists and antagonists uncover that BR receptor–co-receptor signalling complexes can recognize chemically diverse BRs, introducing an additional, intriguing layer of BR signalling regulation.</p>

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A mechanistic framework for the recognition of chemically diverse brassinosteroids by BRI1-family receptor kinases

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年8月5日

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  • Alberto Caregnato,
  • Houming Chen,
  • Miroslav Kvasnica,
  • Ulrich Hohmann,
  • Jana Oklestkova,
  • Karoll Ferrer,
  • Larissa Broger,
  • Ludwig A. Hothorn,
  • Miroslav Strnad,
  • Michael Hothorn

摘要

Brassinosteroids (BRs) are chemically diverse plant steroid hormones produced via a branched biosynthetic pathway. The potent BR brassinolide is sensed by the membrane receptor kinase BRI1 and a SERK co-receptor, but the physiological functions of other abundant BRs remain to be characterized. Here we present quantitative binding kinetics for 4 Arabidopsis thaliana BR receptors and 15 BRs, which define the key chemical features required for high-affinity receptor binding, ligand positioning and co-receptor recognition. BRI1, BRL1 and BRL3 share overlapping ligand preferences, whereas BRL2 binds C28 BRs with moderate affinity. Structural analyses of BR-bound BRI1 and BRL3 ectodomains combined with extensive in vitro and in vivo mutagenesis studies reveal a high structural plasticity of the hormone-binding pocket. Functional assays using structure-based BR agonists and antagonists uncover that BR receptor–co-receptor signalling complexes can recognize chemically diverse BRs, introducing an additional, intriguing layer of BR signalling regulation.