Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/19/2010
Publication Date: 9/20/2010
Citation: Chiu, L., Zhou, X., Burke, S., Wu, X., Prior, R.L., Li, L. 2010. The purple cauliflower arises from activation of a MYB transcription factor. Plant Physiology. 154:1470-1480. Interpretive Summary: Vegetables and fruits are fundamental components of human diets. Colored vegetables and fruits have gained an increasing interest as functional foods, owing to the high levels of plant pigments with potent nutritional and health-promoting effects. In order to gain a better understanding the regulatory mechanisms underlying anthocyanin biosynthesis, we have studied a very eye-catching purple cauliflower mutant. Through candidate gene analysis and fine mapping, we have isolated the Purple gene responsible for the mutation and found that it encodes a R2R3-MYB transcription factor. DNA sequence analysis reveals that the mutation is caused by a transposon insertion in the promoter region of the Purple gene to generate novel regulatory motif in activating the gene expression. The resulting overexpresson of the Purple gene upregulates the expression of a subset of anthocyanin biosynthetic genes to produce the striking mutant phenotype. Successful isolation of the Purple gene provides important information in understanding the regulation of anthocyanin accumulation for breeding Brassica vegetables with enhanced health-promoting properties and visual appeal. Our discovery also demonstrates the involvement of transposable elements in gene regulation for phenotypic change in plants.
Technical Abstract: Anthocyanins are responsible for the color of many flowers, fruits, and vegetables. An interesting and unique Purple (Pr) gene mutation in cauliflower confers an abnormal pattern of anthocyanin accumulation, giving the striking mutant phenotype of intense purple color in curds and a few other tissues. To unravel the nature of the Pr mutation in cauliflower, we isolated the Pr gene via a combination of candidate gene analysis and fine-mapping. Pr encoded a R2R3 MYB transcription factor that exhibited tissue-specific expression, consistent with an abnormal anthocyanin accumulation pattern in the mutant. Transgenic Arabidopsis and cauliflower plants expressing the Pr-D allele recapitulated the mutant phenotype, confirming the isolation of the Pr gene. Up-regulation of Pr specifically activated a bHLH transcription factor and a subset of anthocyanin structural genes (BoF3’H, BoDFR, and BoLDOX ) to confer ectopic accumulation of pigments in the purple cauliflower. Our results indicate that the genetic variation including a Harbinger DNA transposon insertion in the upstream regulatory region of the Pr-D allele is responsible for the up-regulation of the Pr gene in inducing phenotypic change in the plant. The successful isolation of Pr provides important information on the regulatory control of anthocyanin biosynthesis in Brassica vegetables, and offers a genetic resource for development of new varieties with enhanced health-promoting properties and visual appeal.