title: The abi1-1 mutation blocks ABA signaling downstream of cADPR action.
abstract: Arabidopsis thaliana abscisic acid insensitive 1-1 (abi1-1) is a dominant mutant that is insensitive to the inhibition of germination and growth by the plant hormone, abscisic acid (ABA). The mutation severely decreases the catalytic activity of the ABI1 type 2C protein phosphatase (PP2C). However, the site of action of the abi1-1/ABI1 in the ABA signal transduction pathway has not yet been determined. Using single cell assays, we showed that microinjecting mutant abi1-1 protein inhibited the activation of RD29A-GUS and KIN2-GUS in response to ABA, cyclic ADP-ribose (cADPR), and Ca2+. The inhibitory effect of the mutant protein, however, was reversed by co-microinjection of an excess amount of the ABI1 protein. In transgenic Arabidopsis plants, overexpression of abi1-1 rendered the plants insensitive to ABA during germination, whereas overexpression of ABI1 did not have any apparent effect. Moreover, transgenic plants overexpressing abi1-1 were blocked in the induction of ABA-responsive genes; however, overexpression of ABI1 did not affect gene expression. Taken together, our results demonstrate that abi1-1 is likely to be a dominant negative mutation and ABI1 likely acts downstream of cADPR in the ABA-signaling pathway. Our results on ABI1 overexpression in Arabidopsis are not compatible with a negative regulatory role of this phosphatase in ABA responses.
authors.affiliation: Laboratory of Plant Molecular Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Wu
authors.forename: Juan Pablo
authors.initials: JP
authors.lastname: Sanchez
authors.forename: Luis
authors.initials: L
authors.lastname: Lopez-Molina
authors.forename: Axel
authors.initials: A
authors.lastname: Himmelbach
authors.forename: Erwin
authors.initials: E
authors.lastname: Grill
authors.forename: Nam-Hai
authors.initials: NH
authors.lastname: Chua
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D036563:Cyclic ADP-Ribose / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D018525:Germination / Q000187:drug effects; D005966:Glucuronidase / Q000235:genetics / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified; D000071636:Protein Phosphatase 2C; D012639:Seeds / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D036563:Cyclic ADP-Ribose; C075575:KIN 2 protein, Arabidopsis; D000040:Abscisic Acid; C087434:ABI1 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases; D000071636:Protein Phosphatase 2C; D005966:Glucuronidase; D002118:Calcium