title: Isolation and characterization of GtMYBP3 and GtMYBP4, orthologues of R2R3-MYB transcription factors that regulate early flavonoid biosynthesis, in gentian flowers.
abstract: Flavonoids are one of the major plant pigments for flower colour. Not only coloured anthocyanins, but also co-pigment flavones or flavonols, accumulate in flowers. To study the regulation of early flavonoid biosynthesis, two R2R3-MYB transcription factors, GtMYBP3 and GtMYBP4, were identified from the petals of Japanese gentian (Gentiana triflora). Phylogenetic analysis showed that these two proteins belong to the subgroup 7 clade (flavonol-specific MYB), which includes Arabidopsis AtMYB12, grapevine VvMYBF1, and tomato SlMYB12. Gt   MYBP3 and Gt   MYBP4 transcripts were detected specifically in young petals and correlated with the profiles of flavone accumulation. Transient expression assays showed that GtMYBP3 and GtMYBP4 enhanced the promoter activities of early biosynthetic genes, including flavone synthase II (FNSII) and flavonoid 3'-hydroxylase (F3'H), but not the late biosynthetic gene, flavonoid 3',5'-hydroxylase (F3'5'H). GtMYBP3 also enhanced the promoter activity of the chalcone synthase (CHS) gene. In transgenic Arabidopsis, overexpression of Gt   MYBP3 and Gt   MYBP4 activated the expression of endogenous flavonol biosynthesis genes and led to increased flavonol accumulation in seedlings. In transgenic tobacco petals, overexpression of Gt   MYBP3 and Gt   MYBP4 caused decreased anthocyanin levels, resulting in pale flower colours. Gt   MYBP4-expressing transgenic tobacco flowers also showed increased flavonols. As far as is known, this is the first functional characterization of R2R3-MYB transcription factors regulating early flavonoid biosynthesis in petals.
authors.affiliation: Iwate Biotechnology Research Center, 22-174-4 Narita, Kitakami, Iwate 024-0003,  Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakatsuka
authors.forename: Misa
authors.initials: M
authors.lastname: Saito
authors.forename: Eri
authors.initials: E
authors.lastname: Yamada
authors.forename: Kohei
authors.initials: K
authors.lastname: Fujita
authors.forename: Yuko
authors.initials: Y
authors.lastname: Kakizaki
authors.forename: Masahiro
authors.initials: M
authors.lastname: Nishihara
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D020869:Gene Expression Profiling; D030012:Gentiana / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D014157:Transcription Factors