RESUMEN
Nearly all flowering plants produce red/violet anthocyanin pigments. Caryophyllales is the only order containing families that replace anthocyanins with unrelated red and yellow betalain pigments. Close biological correlation of pigmentation patterns suggested that betalains might be regulated by a conserved anthocyanin-regulating transcription factor complex consisting of a MYB, a bHLH and a WD repeat-containing protein (the MBW complex). Here we show that a previously uncharacterized anthocyanin MYB-like protein, Beta vulgaris MYB1 (BvMYB1), regulates the betalain pathway in beets. Silencing BvMYB1 downregulates betalain biosynthetic genes and pigmentation, and overexpressing BvMYB1 upregulates them. However, unlike anthocyanin MYBs, BvMYB1 will not interact with bHLH members of heterologous anthocyanin MBW complexes because of identified nonconserved residues. BvMYB1 resides at the historic beet pigment-patterning locus, Y, required for red-fleshed beets. We show that Y and y express different levels of BvMYB1 transcripts. The co-option of a transcription factor regulating anthocyanin biosynthesis would be an important evolutionary event allowing betalains to largely functionally replace anthocyanins.
Asunto(s)
Beta vulgaris/genética , Betalaínas/biosíntesis , Regulación de la Expresión Génica de las Plantas/genética , Genes de Plantas , Pigmentación/genética , Proteínas de Plantas/genética , Factores de Transcripción/genética , Agrobacterium/genética , Secuencia de Aminoácidos , Antocianinas/biosíntesis , Secuencia de Bases , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Beta vulgaris/crecimiento & desarrollo , Beta vulgaris/metabolismo , Silenciador del Gen , Datos de Secuencia Molecular , Complejos Multiproteicos , Proteínas de Plantas/metabolismo , Plantas Modificadas Genéticamente , Estructura Terciaria de Proteína , ARN Mensajero/biosíntesis , ARN de Planta/biosíntesis , Alineación de Secuencia , Homología de Secuencia , Factores de Transcripción/metabolismo , Transcripción Genética , Transformación GenéticaRESUMEN
Anthocyanins are red and violet pigments that color flowers, fruits and epidermal tissues in virtually all flowering plants. A single order, Caryophyllales, contains families in which an unrelated family of pigments, the betalains, color tissues normally pigmented by anthocyanins. Here we show that CYP76AD1 encoding a novel cytochrome P450 is required to produce the red betacyanin pigments in beets. Gene silencing of CYP76AD1 results in loss of red pigment and production of only yellow betaxanthin pigment. Yellow betalain mutants are complemented by transgenic expression of CYP76AD1, and an insertion in CYP76AD1 maps to the R locus that is responsible for yellow versus red pigmentation. Finally, expression of CYP76AD1 in yeast verifies its position in the betalain biosynthetic pathway. Thus, this cytochrome P450 performs the biosynthetic step that provides the cyclo-DOPA moiety of all red betacyanins. This discovery will contribute to our ability to engineer this simple, nutritionally valuable pathway into heterologous species.
