title: Accumulation of the transcription factor ABA-insensitive (ABI)4 is tightly regulated post-transcriptionally.
abstract: ABA-INSENSITIVE (ABI)4 is a transcription factor implicated in response to ABA in maturing seeds, and seedling responses to ABA, salt, and sugar. Previous studies have shown that ABI4 transcripts are high in seeds and in seedlings exposed to high concentrations of glucose and, to a lesser extent, osmotic agents and ABA, but that transcript levels are very low through most of vegetative growth. This study examined ABI4 protein accumulation indirectly, using transgenic lines expressing fusions to GFP and GUS. The GFP fusions were active, but undetectable visually or immunologically. Comparison of transcript and activity levels for GUS expression showed that inclusion of the ABI4 coding sequence reduced the ratio of activity to transcript ∼40-fold when driven by the CaMV 35S promoter, and nearly 150-fold when controlled by the ABI4 promoter. At least part of this discrepancy is due to proteasomal degradation of ABI4, resulting in a half-life of 5-6 h for the ABI4-GUS fusion. Comparison of the spatial localization of transcripts and fusion proteins indicated that the protein preferentially accumulated in roots such that transcript and protein distribution had little similarity. The components mediating targeting to the proteasome or other mechanisms of spatial restriction have not yet been identified, but several domains of ABI4 appear to contribute to its instability.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA 93106, USA. finkelst@lifesci.ucsb.edu
authors.forename: Ruth
authors.initials: R
authors.lastname: Finkelstein
authors.forename: Tim
authors.initials: T
authors.lastname: Lynch
authors.forename: Wendy
authors.initials: W
authors.lastname: Reeves
authors.forename: Michelle
authors.initials: M
authors.lastname: Petitfils
authors.forename: Mike
authors.initials: M
authors.lastname: Mostachetti
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D005966:Glucuronidase / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006207:Half-Life; D010937:Plant Growth Regulators / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012639:Seeds / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: C470421:ABI4 protein, Arabidopsis; D029681:Arabidopsis Proteins; D010937:Plant Growth Regulators; D010940:Plant Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D000040:Abscisic Acid; D005966:Glucuronidase