title: TRANSPARENT TESTA1 interacts with R2R3-MYB factors and affects early and late steps of flavonoid biosynthesis in the endothelium of Arabidopsis thaliana seeds.
abstract: Wild type seed coats of Arabidopsis thaliana are brown due to the accumulation of proanthocyanidin pigments (PAs). The pigmentation requires activation of phenylpropanoid biosynthesis genes and mutations in some of these genes cause a yellow appearance of seeds, termed transparent testa (tt) phenotype. The TT1 gene encodes a WIP-type zinc finger protein and is expressed in the seed coat endothelium where most of the PAs accumulate in wild type plants. In this study we show that TT1 is not only required for correct expression of PA-specific genes in the seed coat, but also affects CHS, encoding the first enzyme of flavonoid biosynthesis. Many steps of this pathway are controlled by complexes of MYB and BHLH proteins with the WD40 factor TTG1. We demonstrate that TT1 can interact with the R2R3 MYB protein TT2 and that ectopic expression of TT2 can partially restore the lack in PA production in tt1. Reduced seed coat pigmentation was obtained using a TT1 variant lacking nuclear localisation signals. Based on our results we propose that the TT2/TT8/TTG1 regulon may also comprise early genes like CHS and discuss steps to further unravel the regulatory network controlling flavonoid accumulation in endothelium cells during A. thaliana seed development.
authors.affiliation: Department of Biology, Chair of Genome Research, Bielefeld University, D-33594 Bielefeld, Germany.
authors.forename: Ingo
authors.initials: I
authors.lastname: Appelhagen
authors.forename: Gui-Hua
authors.initials: GH
authors.lastname: Lu
authors.forename: Gunnar
authors.initials: G
authors.lastname: Huep
authors.forename: Elmon
authors.initials: E
authors.lastname: Schmelzer
authors.forename: Bernd
authors.initials: B
authors.lastname: Weisshaar
authors.forename: Martin
authors.initials: M
authors.lastname: Sagasser
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005419:Flavonoids / Q000096:biosynthesis*; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D056426:Genetic Loci; D009154:Mutation; D010641:Phenotype; D010858:Pigmentation; D018085:Regulon; D012639:Seeds / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D005419:Flavonoids; C451324:TT2 protein, Arabidopsis; C417767:TT8 protein, Arabidopsis; C121067:TTG1 protein, Arabidopsis