Title: Transcription Factor Families Regulate the Anthocyanin Biosynthetic Pathway in Capsicum Authors
Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 14, 2009
Publication Date: March 1, 2009
Citation: Lightbourn, G., Winkel, B., Griesbach, R.J., Stommel, J.R. 2009. Transcription Factor Families Regulate the Anthocyanin Biosynthetic Pathway in Capsicum. Journal of the American Society for Horticultural Science. 134:244-251. Interpretive Summary: Many visible characteristics in plants such as color are the outcome of a biosynthetic pathway. Two types of genes are involved in the expression of a biosynthetic pathway. Structural genes provide the information to create the enzymes that are responsible for each step in the pathway. Regulatory genes control whether the structural genes are turned on or off. We have developed a model system using a pepper plant with black leaves to study how regulatory genes control the function of structural genes for the anthocyanin biosynthetic pathway. Anthocyanins are the pigments responsible for purple to black color in pepper. Using pepper plants that accumulate anthocyanin pigment in flowers, fruits and leaves and pepper plants that do not accumulate anthocyanin in these tissues, we determined which anthocyanin-related structural and regulatory genes control anthocyanin accumulation. Our results demonstrated that the action of multiple regulatory genes is required to activate structural genes for anthocyanin accumulation in pepper flowers and fruits. Our results further demonstrated that the genetic control of anthocyanin accumulation in leaves differs from that in flowers and fruits. This information on anthocyanin content and genes that influence anthocyanin content will be utilized by scientists to further study and develop novel leaf, stem, and fruit colors in pepper and other food crops and ornamentals where color contributes to product quality.
Technical Abstract: Anthocyanin structural gene transcription requires the expression of at least one member of each of three transcription factor families - MYC, MYB and WD40. These transcription factors form a complex that binds to structural gene promoters, thereby modulating gene expression. Capsicum annuum displays a wide spectrum of tissue-specific anthocyanin pigmentation, making it a useful model for the study of anthocyanin accumulation. In order to determine the genetic basis for tissue-specific pigmentation, we evaluated the expression of anthocyanin biosynthetic (Chs, Dfr, Ans) and regulatory (MycA, MybA, Wd) genes in flower, fruit and foliar tissue from pigmented and non-pigmented genotypes. No differences were observed in expression of the Wd40 gene among these tissues. However, in all cases, biosynthetic gene transcript levels were considerably higher in anthocyanin pigmented tissue than in non-pigmented tissues. MybA and MycA transcript levels were also substantially higher in anthocyanin pigmented fruit and floral tissues. Sequence analysis of the products of 5' and/or 3' RACE experiments indicated that the MybA and MycA transcripts in these tissues are each derived from at least two different genes. In contrast to the situation in flowers and fruit, differential expression of MybA and MycA was not observed in foliar tissue, suggesting that different mechanisms contribute to the regulation of anthocyanin biosynthesis in different parts of the Capsicum plant.