RESUMO
Wild tomato species represent a rich gene pool for numerous desirable traits lost during domestication. Here, we exploited an introgression population representing wild desert-adapted species and a domesticated cultivar to establish the genetic basis of gene expression and chemical variation accompanying the transfer of wild-species-associated fruit traits. Transcriptome and metabolome analysis of 580 lines coupled to pathogen sensitivity assays resulted in the identification of genomic loci associated with levels of hundreds of transcripts and metabolites. These associations occurred in hotspots representing coordinated perturbation of metabolic pathways and ripening-related processes. Here, we identify components of the Solanum alkaloid pathway, as well as genes and metabolites involved in pathogen defense and linking fungal resistance with changes in the fruit ripening regulatory network. Our results outline a framework for understanding metabolism and pathogen resistance during tomato fruit ripening and provide insights into key fruit quality traits.
Assuntos
Resistência à Doença/genética , Metaboloma/genética , Solanum lycopersicum/genética , Transcriptoma/genética , Alcaloides/genética , Domesticação , Frutas/genética , Frutas/crescimento & desenvolvimento , Frutas/parasitologia , Fungos/genética , Fungos/patogenicidade , Regulação da Expressão Gênica de Plantas/genética , Solanum lycopersicum/crescimento & desenvolvimento , Solanum lycopersicum/microbiologia , Redes e Vias Metabólicas/genética , Fenótipo , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Solanum/genética , Solanum/microbiologiaRESUMO
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.
Assuntos
Antocianinas/metabolismo , Metiltransferases/metabolismo , Plântula/metabolismo , Solanum lycopersicum/metabolismo , Antocianinas/genética , Flavonoides/metabolismo , Frutas/genética , Frutas/metabolismo , Regulação da Expressão Gênica de Plantas , Inativação Gênica , Hipocótilo/genética , Hipocótilo/metabolismo , Solanum lycopersicum/genética , Metilação , Metiltransferases/genética , Dados de Sequência Molecular , Família Multigênica , Filogenia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plantas Geneticamente Modificadas , Plântula/genética , Especificidade por SubstratoRESUMO
Strawberry (Fragaria × ananassa) fruits contain high concentrations of flavonoids. In unripe strawberries, the flavonoids are mainly represented by proanthocyanidins (PAs), while in ripe fruits the red-coloured anthocyanins also accumulate. Most of the structural genes leading to PA biosynthesis in strawberry have been characterized, but no information is available on their transcriptional regulation. In Arabidopsis thaliana the expression of the PA biosynthetic genes is specifically induced by a ternary protein complex, composed of AtTT2 (AtMYB123), AtTT8 (AtbHLH042) and AtTTG1 (WD40-repeat protein). A strategy combining yeast-two-hybrid screening and agglomerative hierarchical clustering of transcriptomic and metabolomic data was undertaken to identify strawberry PA regulators. Among the candidate genes isolated, four were similar to AtTT2, AtTT8 and AtTTG1 (FaMYB9/FaMYB11, FabHLH3 and FaTTG1, respectively) and two encode putative negative regulators (FaMYB5 and FabHLH3∆). Interestingly, FaMYB9/FaMYB11, FabHLH3 and FaTTG1 were found to complement the tt2-1, tt8-3 and ttg1-1 transparent testa mutants, respectively. In addition, they interacted in yeast and activated the Arabidopsis BANYULS (anthocyanidin reductase) gene promoter when coexpressed in Physcomitrella patens protoplasts. Taken together, these results demonstrated that FaMYB9/FaMYB11, FabHLH3 and FaTTG1 are the respective functional homologues of AtTT2, AtTT8 and AtTTG1, providing new tools for modifying PA content and strawberry fruit quality.
