title: Expression of the R2R3-MYB transcription factor TaMYB14 from Trifolium arvense activates proanthocyanidin biosynthesis in the legumes Trifolium repens and Medicago sativa.
abstract: Proanthocyanidins (PAs) are oligomeric flavonoids and one group of end products of the phenylpropanoid pathway. PAs have been reported to be beneficial for human and animal health and are particularly important in pastoral agricultural systems for improved animal production and reduced greenhouse gas emissions. However, the main forage legumes grown in these systems, such as Trifolium repens and Medicago sativa, do not contain any substantial amounts of PAs in leaves. We have identified from the foliar PA-accumulating legume Trifolium arvense an R2R3-MYB transcription factor, TaMYB14, and provide evidence that this transcription factor is involved in the regulation of PA biosynthesis in legumes. TaMYB14 expression is necessary and sufficient to up-regulate late steps of the phenylpropanoid pathway and to induce PA biosynthesis. RNA interference silencing of TaMYB14 resulted in almost complete cessation of PA biosynthesis in T. arvense, whereas Nicotiana tabacum, M. sativa, and T. repens plants constitutively expressing TaMYB14 synthesized and accumulated PAs in leaves up to 1.8% dry matter. Targeted liquid chromatography-multistage tandem mass spectrometry analysis identified foliar PAs up to degree of polymerization 6 in leaf extracts. Hence, genetically modified M. sativa and T. repens plants expressing TaMYB14 provide a viable option for improving animal health and mitigating the negative environmental impacts of pastoral animal production systems.
authors.affiliation: AgResearch, Ltd., Palmerston North 4442, New Zealand.
authors.forename: Kerry R
authors.initials: KR
authors.lastname: Hancock
authors.forename: Vern
authors.initials: V
authors.lastname: Collette
authors.forename: Karl
authors.initials: K
authors.lastname: Fraser
authors.forename: Margaret
authors.initials: M
authors.lastname: Greig
authors.forename: Hong
authors.initials: H
authors.lastname: Xue
authors.forename: Kim
authors.initials: K
authors.lastname: Richardson
authors.forename: Chris
authors.initials: C
authors.lastname: Jones
authors.forename: Susanne
authors.initials: S
authors.lastname: Rasmussen
mesh_terms: D000595:Amino Acid Sequence; D053898:Biosynthetic Pathways; D002853:Chromatography, Liquid; D019281:Dimerization; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D017343:Genes, Plant / Q000235:genetics; D006801:Humans; D013058:Mass Spectrometry; D000455:Medicago sativa / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D044945:Proanthocyanidins / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014026:Nicotiana / Q000235:genetics; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029921:Trifolium / Q000235:genetics / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D044945:Proanthocyanidins; D012333:RNA, Messenger; D014157:Transcription Factors; C013221:proanthocyanidin