title: Functional analysis of TaABF1 during abscisic acid and gibberellin signalling in aleurone cells of cereal grains.
abstract: The wheat transcription factor TaABF1 physically interacts with the protein kinase PKABA1 and mediates both abscisic acid (ABA)-induced and ABA-suppressed gene expression. In bombarded aleurone cells of imbibing grains, the effect of TaABF1 in down-regulating the gibberellin (GA)-inducedAmy32bpromoter was stronger in the presence of exogenous ABA. As these grains contained low levels of endogenous ABA, the effect of TaABF1 may also be mediated by ABA-induced activation even in the absence of exogenous ABA. Levels of TaABF1 protein decreased slightly during imbibition of afterripened grains. However, TaABF1 levels (especially in aleurone layers) were not substantially affected by exogenous ABA or GA, indicating that changes in TaABF1 protein level are not an important part of regulating its role in hormone signalling. We found that TaABF1 was phosphorylatedin vivoin aleurone cells, suggesting a role for post-translational modification in regulating TaABF1 activity. Induction ofAmy32bby overexpression of the transcription factor GAMyb could not be prevented by TaABF1, indicating that TaABF1 acts upstream ofGAMybtranscription in the signalling pathway. Supporting this view, knockdown of TaABF1 by RNA interference resulted in increased expression from theGAMybpromoter. These results are consistent with a model in which TaABF1 is constitutively present in aleurone cells, while its ability to down-regulateGAMybis regulated in response to ABA.
authors.affiliation: Department of Biology, Colby College, 5723 Mayflower Hill, Waterville, ME 04901, USA.
authors.forename: Lauren J
authors.initials: LJ
authors.lastname: Harris
authors.affiliation: Department of Biology, Colby College, 5723 Mayflower Hill, Waterville, ME 04901, USA.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Martinez
authors.affiliation: Department of Biology, Colby College, 5723 Mayflower Hill, Waterville, ME 04901, USA.
authors.forename: Benjamin R
authors.initials: BR
authors.lastname: Keyser
authors.affiliation: Department of Plant Sciences and Plant Pathology, Montana State University, Bozeman, MT 59715, USA.
authors.forename: William E
authors.initials: WE
authors.lastname: Dyer
authors.affiliation: Department of Biology, Colby College, 5723 Mayflower Hill, Waterville, ME 04901, USA.
authors.forename: Russell R
authors.initials: RR
authors.lastname: Johnson
keywords: abscisic acid; germination; gibberellin; imbibition; wheat