BIN2 functions redundantly with other Arabidopsis GSK3-like kinases to regulate brassinosteroid signaling.
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.
Yan
Zhenyan
Z
Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109-1048, USA.
Zhao
Jun
J
Peng
Peng
P
Chihara
Ray K
RK
Li
Jianming
J
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D060406:Brassinosteroids; D002777:Cholestanols / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D018021:Lithium Chloride / Q000494:pharmacology; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional / Q000187:drug effects; D050505:Mutant Proteins / Q000302:isolation & purification / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000187:drug effects; D013260:Steroids, Heterocyclic / Q000378:metabolism*; D013489:Suppression, Genetic / Q000187:drug effects
D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D002777:Cholestanols; D004269:DNA, Bacterial; D038362:Glycogen Synthase Kinase 3; D018021:Lithium Chloride; D050505:Mutant Proteins; D011494:Protein Kinases; D013260:Steroids, Heterocyclic; C036483:T-DNA; C448985:At4g18710 protein, Arabidopsis; C023623:brassinolide