RESUMO
Betalains are tyrosine-derived red-violet and yellow plant pigments known for their antioxidant activity, health-promoting properties, and wide use as food colorants and dietary supplements. By coexpressing three genes of the recently elucidated betalain biosynthetic pathway, we demonstrate the heterologous production of these pigments in a variety of plants, including three major food crops: tomato, potato, and eggplant, and the economically important ornamental petunia. Combinatorial expression of betalain-related genes also allowed the engineering of tobacco plants and cell cultures to produce a palette of unique colors. Furthermore, betalain-producing tobacco plants exhibited significantly increased resistance toward gray mold (Botrytis cinerea), a pathogen responsible for major losses in agricultural produce. Heterologous production of betalains is thus anticipated to enable biofortification of essential foods, development of new ornamental varieties, and innovative sources for commercial betalain production, as well as utilization of these pigments in crop protection.
Assuntos
Antioxidantes/metabolismo , Betalaínas/biossíntese , Produtos Agrícolas/genética , Pigmentação/genética , Vias Biossintéticas/genética , Botrytis/fisiologia , Cor , Produtos Agrícolas/metabolismo , Produtos Agrícolas/microbiologia , Resistência à Doença/genética , Solanum lycopersicum/genética , Solanum lycopersicum/metabolismo , Solanum lycopersicum/microbiologia , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Plantas Geneticamente Modificadas , Solanum melongena/genética , Solanum melongena/metabolismo , Solanum melongena/microbiologia , Solanum tuberosum/genética , Solanum tuberosum/metabolismo , Solanum tuberosum/microbiologia , Nicotiana/citologia , Nicotiana/genética , Nicotiana/metabolismoRESUMO
Betalains are tyrosine-derived red-violet and yellow pigments, found in plants only of the Caryophyllales order. Although much progress has been made in recent years in the understanding of the betalain biosynthetic process, many questions remain open with regards to several of the proposed steps in the pathway. Most conspicuous by its absence is the characterization of the first committed step in the pathway, namely the 3-hydroxylation of tyrosine to form l-3,4-dihydroxyphenylalanine (l-DOPA). We used transcriptome analysis of the betalain-producing plants red beet (Beta vulgaris) and four o'clocks (Mirabilis jalapa) to identify a novel, betalain-related cytochrome P450-type gene, CYP76AD6, and carried out gene silencing and recombinant expression assays in Nicotiana benthamiana and yeast cells to examine its functionality. l-DOPA formation in red beet was found to be redundantly catalyzed by CYP76AD6 together with a known betalain-related enzyme, CYP76AD1, which was previously thought to only catalyze a succeeding step in the pathway. While CYP76AD1 catalyzes both l-DOPA formation and its subsequent conversion to cyclo-DOPA, CYP76AD6 uniquely exhibits only tyrosine hydroxylase activity. The new findings enabled us to metabolically engineer entirely red-pigmented tobacco plants through heterologous expression of three genes taking part in the fully decoded betalain biosynthetic pathway.