Submitted to: Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/1/2003
Publication Date: 12/1/2003
Citation: Farzad, M., Griesbach, R., Hammond, J. Weiss, M., Elmendorf, H. 2003. Differential Expression of Three Key Anthocyanin Biosynthetic Genes in a Color-Changing Flower, Viola Cornuta cv. Yesterday, Today and Tomorrow. Plant Science. 165:1333-1342. Interpretive Summary: Flower color is a major factor in the desirability of ornamental plants, and production of varieties with new flower colors has significant economic impact. Color is largely determined by the amounts of various anthocyanin pigments and co-pigments produced in the flower. Most of the genes in the anthocyanin biosynthetic pathway have been characterized in Petunia, but the regulation of anthocyanin synthesis resulting in different flower colors in other flowers is not well understood. Viola cornuta variety Yesterday, Today and Tomorrow is a plant in which flower color changes over time, in response to environmental factors including light and pollination. The expression of three key genes in the anthocyanin biosynthetic pathway was examined in order to understand the role of light and pollination in regulation of pigment production in this color-changing flower. This study demonstrates that the three genes are regulated differently. These results increase understanding of flower color development, and may facilitate production of flowers with different colors.
Technical Abstract: The natural floral color change in Viola cornuta cv. Yesterday, Today and Tomorrow (YTT) provides an opportunity to examine the expression of genes along the anthocyanin biosynthetic pathway in response to known environmental triggers during ontogeny. We have cloned and sequenced gene fragments from three anthocyanin biosynthetic genes, chalcone synthase (Chs), dihydroflavonol 4-reductase (Dfr) and anthocyanidin synthase (Ans). Using quantitative RT-PCR we have determined that Chs and Dfr are highly expressed in Stage I white YTT flowers and undergo only moderate increases in expression (25% and 56% respectively) during the transition to Stage II lavender and Stage III purple flowers. In contrast, Ans is expressed at low levels in Stage I flowers and undergoes a dramatic increase (302%) in expression over ontogeny. Interestingly, expression of all three genes is significantly lower in the absence of two environmental triggers, pollination and light, both of which are necessary for floral color change in Viola cornuta. Our results demonstrate the presence of at least two regulated steps in Viola cornuta anthocyanin biosynthesis: an early step influenced by pollination and light induces expression of earlier genes (Chs and Dfr) in the anthocyanin biosynthetic pathway, and is necessary but insufficient for floral color change, followed by a second step that affects floral color change by inducing expression of later genes (Ans). We have thus identified important environmental cues and developed molecular tools that establish Viola cornuta as a new model system for the study of the regulation of natural floral color change.