title: Enhanced ethylene responsiveness in the Arabidopsis eer1 mutant results from a loss-of-function mutation in the protein phosphatase 2A A regulatory subunit, RCN1.
abstract: Ethylene signaling in Arabidopsis begins with a family of five ethylene receptors that regulate the activity of the Raf-like kinase, CTR1. Recent work to identify novel factors required for modulating ethylene signaling resulted in the isolation of enhanced ethylene response 1 (eer1), a mutant that displays both increased sensitivity and increased amplitude of response to ethylene. Molecular cloning of eer1 reveals that its mutant phenotype results from a loss-of-function mutation in the previously characterized RCN1, one of three PP2A A regulatory subunits in Arabidopsis. Our analysis shows that neither RCN1 expression nor PP2A activity is regulated by ethylene. Instead, we found that Arabidopsis PP2A-1C, a PP2A catalytic subunit previously characterized as interacting with RCN1, associates strongly with the kinase domain of CTR1 in vitro. This likely represents a role for PP2A in modulation of CTR1 activity because an in vitro kinase assay did not reveal phosphorylation of either RCN1 or PP2A-1C by CTR1, indicating that neither of them is a substrate for CTR1. PP2A activity is required for Ras-dependent activation of mammalian Raf, with reductions in PP2A activity significantly compromising the effectiveness of this mechanism. Our genetic and biochemical results suggest that a similar requirement for PP2A activity exists for ethylene signaling, with loss-of-function mutations affecting PP2A activity possibly reducing the effectiveness of CTR1 activation, thus lowering the threshold required for manifestation of ethylene response.
authors.affiliation: Department of Biochemistry, University of California-Riverside, Riverside, California, CA 92521, USA. paul.larsen@ucr.edu
authors.forename: Paul Brian
authors.initials: PB
authors.lastname: Larsen
authors.forename: Jesse Daniel
authors.initials: JD
authors.lastname: Cancel
mesh_terms: D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D003001:Cloning, Molecular; D005030:Ethylenes / Q000494:pharmacology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D054648:Protein Phosphatase 2; D017434:Protein Structure, Tertiary; D036226:Seedlings / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D013379:Substrate Specificity
chemical_list: D029681:Arabidopsis Proteins; D005030:Ethylenes; C036216:ethylene; D011494:Protein Kinases; C477753:CTR1 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C478612:RCN1 protein, Arabidopsis