Enhanced ethylene responsiveness in the Arabidopsis eer1 mutant results from a loss-of-function mutation in the protein phosphatase 2A A regulatory subunit, RCN1.
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.
Larsen
Paul Brian
PB
Department of Biochemistry, University of California-Riverside, Riverside, California, CA 92521, USA. paul.larsen@ucr.edu
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Jesse Daniel
JD
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
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