title: An O-methyltransferase modifies accumulation of methylated anthocyanins in seedlings of tomato.
abstract: Anthocyanins contribute to the appearance of fruit by conferring to them a red, blue or purple colour. In a food context, they have also been suggested to promote consumer health. In purple tomato tissues, such as hypocotyls, stems and purple fruits, various anthocyanins accumulate. These molecules have characteristic patterns of modification, including hydroxylations, methylations, glycosylations and acylations. The genetic basis for many of these modifications has not been fully elucidated, and nor has their role in the functioning of anthocyanins. In this paper, AnthOMT, an O-methyltransferase (OMT) mediating the methylation of anthocyanins, has been identified and functionally characterized using a combined metabolomics and transcriptomics approach. Gene candidates were selected from the draft tomato genome, and their expression was subsequently monitored in a tomato seedling system comprising three tissues and involving several time points. In addition, we also followed gene expression in wild-type red and purple transgenic tomato fruits expressing Rosea1 and Delila transcription factors. Of the 57 candidates identified, only a single OMT gene showed patterns strongly correlating with both accumulation of anthocyanins and expression of anthocyanin biosynthesis genes. This candidate (AnthOMT) was compared to a closely related caffeoyl CoA OMT by recombinant expression in Escherichia coli, and then tested for substrate specificity. AnthOMT showed a strong affinity for glycosylated anthocyanins, while other flavonoid glycosides and aglycones were much less preferred. Gene silencing experiments with AnthOMT resulted in reduced levels of the predominant methylated anthocyanins. This confirms the role of this enzyme in the diversification of tomato anthocyanins.
authors.affiliation: BU Biosciences, Plant Research International, Wageningen University and Research Centre, PO Box 16, 6700 AA, Wageningen, The Netherlands; Netherlands Consortium for Systems Biology, PO Box 94215, 1090 GE, Amsterdam, The Netherlands; Netherlands Metabolomics Centre, Einsteinweg 55, 2333 CC, Leiden, The Netherlands.
authors.forename: Maria Victoria
authors.initials: MV
authors.lastname: Gomez Roldan
authors.forename: Nikolay
authors.initials: N
authors.lastname: Outchkourov
authors.forename: Adèle
authors.initials: A
authors.lastname: van Houwelingen
authors.forename: Michiel
authors.initials: M
authors.lastname: Lammers
authors.forename: Irene
authors.initials: I
authors.lastname: Romero de la Fuente
authors.forename: Noa
authors.initials: N
authors.lastname: Ziklo
authors.forename: Asaph
authors.initials: A
authors.lastname: Aharoni
authors.forename: Robert D
authors.initials: RD
authors.lastname: Hall
authors.forename: Jules
authors.initials: J
authors.lastname: Beekwilder
mesh_terms: D000872:Anthocyanins / Q000235:genetics / Q000378:metabolism*; D005419:Flavonoids / Q000378:metabolism; D005638:Fruit / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D018546:Hypocotyl / Q000235:genetics / Q000378:metabolism; D018551:Solanum lycopersicum / Q000235:genetics / Q000378:metabolism*; D008745:Methylation; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D036226:Seedlings / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000872:Anthocyanins; D005419:Flavonoids; D010940:Plant Proteins; D008780:Methyltransferases
keywords: Solanum lycopersicum; anthocyanins; hypocotyls; methylation; methyltransferase; tomato