Carotenoids are yellow, orange, and red pigments that contribute to the beautiful colors and nutritive value of many flowers (e.g., daffodils, daylilies, sunflowers) and fruits (e.g., oranges, tomatoes, mangos). They also serve an important function in the ecology and evolution of plants by attracting pollinators and seed dispersers.
The incredible diversity of carotenoid pigmentation patterns in angiosperm flowers and fruits is largely determined by differential expression of the carotenoid biosynthetic genes. And often, this differential expression involves coordinated up- or down-regulation of multiple structural genes or the entire carotenoid biosynthetic pathway, indicating the critical role of transcription factors (TFs) in the generation of color variation. However, although the structural genes in the highly conserved carotenoid biosynthetic pathway have been extensively characterized in multiple plant systems, little is known about the TFs that control the expression of these structural genes. In fact, not a single TF regulating carotenoid pigmentation during flower development has been reported before our study. Lack of such knowledge is a significant impediment to understanding the molecular basis of flower and fruit coloration, the evolution of color diversity, and the genetic control of plant-pollinator interactions.
By analyzing an EMS mutant with reduced carotenoid pigmentation (rcp) in the nectar guides, we have identified the first TF, RCP1, that regulates the entire carotenoid biosynthetic pathway during M. lewisii flower development. Currently we are characterizing additional EMS mutants with floral carotenoid pigmentation phenotypes to discover other components of the carotenoid transcriptional regulatory complex .
The discovery and characterization of this transcriptional regulatory complex are crucial to understanding how carotenoid pigmentation is regulated during flower development and how carotenoid-based flower color variation is generated during evolution. Furthermore, the TFs that directly regulate the carotenoid biosynthetic pathway will be obvious targets for genetic manipulation in crop plants to enhance carotenoid production.