BIN2 functions redundantly with other Arabidopsis GSK3-like kinases to regulate brassinosteroid signaling

Plant Physiol. 2009 Jun;150(2):710-21. doi: 10.1104/pp.109.138099. Epub 2009 Apr 24.

Abstract

GLYCOGEN SYNTHASE KINASE3 (GSK3) is a highly conserved serine/threonine kinase involved in a variety of developmental signaling processes. The Arabidopsis (Arabidopsis thaliana) genome encodes 10 GSK3-like kinases that are clustered into four groups. Forward genetic screens have so far uncovered eight mutants, all of which carry gain-of-function mutations in BRASSINOSTEROID-INSENSITIVE2 (BIN2), one of the three members in group II. Genetic and biochemical studies have implicated a negative regulatory role for BIN2 in brassinosteroid (BR) signaling. Here, we report the identification of eight ethyl methanesulfonate-mutagenized loss-of-function bin2 alleles and one T-DNA insertional mutation each for BIN2 and its two closest homologs, BIN2-Like1 and BIN2-Like2. Our genetic, biochemical, and physiological assays revealed that despite functional redundancy, BIN2 plays a dominant role among the three group II members in regulating BR signaling. Surprisingly, the bin2bil1bil2 triple T-DNA insertional mutant still responds to BR and accumulates a more phosphorylated form of a BIN2 substrate than the wild-type plant. Using the specific GSK3 inhibitor lithium chloride, we have provided strong circumstantial evidence for the involvement of other Arabidopsis GSK3-like kinases in BR signaling. Interestingly, lithium chloride treatment was able to suppress the gain-of-function bin2-1 mutation but had a much weaker effect on a strong BR receptor mutant, suggesting the presence of a BIN2-independent regulatory step downstream of BR receptor activation.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / drug effects
  • Arabidopsis / enzymology*
  • Arabidopsis Proteins / chemistry
  • Arabidopsis Proteins / metabolism*
  • Brassinosteroids
  • Cholestanols / metabolism*
  • DNA, Bacterial / genetics
  • Glycogen Synthase Kinase 3 / metabolism*
  • Lithium Chloride / pharmacology
  • Molecular Sequence Data
  • Mutagenesis, Insertional / drug effects
  • Mutant Proteins / isolation & purification
  • Mutant Proteins / metabolism
  • Mutation / genetics
  • Phosphorylation / drug effects
  • Protein Kinases / metabolism*
  • Sequence Homology, Amino Acid
  • Signal Transduction* / drug effects
  • Steroids, Heterocyclic / metabolism*
  • Suppression, Genetic / drug effects

Substances

  • Arabidopsis Proteins
  • Brassinosteroids
  • Cholestanols
  • DNA, Bacterial
  • Mutant Proteins
  • Steroids, Heterocyclic
  • T-DNA
  • Protein Kinases
  • BIN2 protein, Arabidopsis
  • Glycogen Synthase Kinase 3
  • Lithium Chloride
  • brassinolide

Associated data

  • RefSeq/NP_180655
  • RefSeq/NP_193606
  • RefSeq/NP_973771