BAK1 is involved in AtRALF1-induced inhibition of root cell expansion

PLoS Genet. 2017 Oct 13;13(10):e1007053. doi: 10.1371/journal.pgen.1007053. eCollection 2017 Oct.


The rapid alkalinization factor (RALF) peptide negatively regulates cell expansion, and an antagonistic relationship has been demonstrated between AtRALF1, a root-specific RALF isoform in Arabidopsis, and brassinosteroids (BRs). An evaluation of the response of BR signaling mutants to AtRALF1 revealed that BRI1-associated receptor kinase1 (bak1) mutants are insensitive to AtRALF1 root growth inhibition activity. BAK1 was essential for the induction of AtRALF1-responsive genes but showed no effect on the mobilization of Ca2+ and alkalinization responses. Homozygous plants accumulating AtRALF1 and lacking the BAK1 gene did not exhibit the characteristic semi-dwarf phenotype of AtRALF1-overexpressors. Biochemical evidence indicates that AtRALF1 and BAK1 physically interact with a Kd of 4.6 μM and acridinium-labeled AtRALF1 was used to demonstrate that part of the specific binding of AtRALF1 to intact seedlings and to a microsomal fraction derived from the roots of Arabidopsis plants is BAK1-dependent. Moreover, AtRALF1 induces an increase in BAK1 phosphorylation, suggesting that the binding of AtRALF1 to BAK1 is functional. These findings show that BAK1 contains an additional AtRALF1 binding site, indicating that this protein may be part of a AtRALF1-containing complex as a co-receptor, and it is required for the negative regulation of cell expansion.

MeSH terms

  • Arabidopsis / genetics*
  • Arabidopsis / growth & development
  • Arabidopsis Proteins / genetics*
  • Carrier Proteins / genetics
  • Cell Cycle / genetics
  • Cell Proliferation / genetics
  • Gene Expression Regulation, Plant / genetics
  • Peptide Hormones / genetics*
  • Phenotype
  • Phosphorylation
  • Plant Growth Regulators / metabolism
  • Plant Roots / genetics*
  • Plant Roots / growth & development
  • Protein-Serine-Threonine Kinases / genetics*
  • Signal Transduction / genetics


  • Arabidopsis Proteins
  • Carrier Proteins
  • Peptide Hormones
  • Plant Growth Regulators
  • RALF1 protein, Arabidopsis
  • BAK1 protein, Arabidopsis
  • Protein-Serine-Threonine Kinases

Grant support

This research was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (2014/14487-1, FAPESP), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). KD was supported by fellowship from FAPESP (2011/17264-5, 2012/13658-1). PHOC, JCGA, TB, ALS and FAOM were supported by fellowships from CNPq and CAPES. MCSF and DSM are research fellows of CNPq. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.