Transcriptomic Analysis of Leaf in Tree Peony Reveals Differentially Expressed Pigments Genes

Anthocyanins represent the major red, purple, violet and blue pigments in many flowers and fruits. They attract pollinators and seed dispersers and defend plants against abiotic and biotic stresses. Anthocyanins are produced by a specific branch of the flavonoid pathway, which is differently regulated in monocot and dicot species. In the monocot maize, the anthocyanin biosynthesis genes are activated as a single unit by a ternary complex of MYB-bHLH-WD40 transcription factors (MBW complex). In the dicot Arabidopsis, anthocyanin biosynthesis genes can be divided in two subgroups: early biosynthesis genes (EBGs) are activated by co-activator independent R2R3-MYB transcription factors, whereas late biosynthesis genes (LBGs) require an MBW complex. In addition to this, a complex regulatory network of positive and negative feedback mechanisms controlling anthocyanin synthesis in Arabidopsis has been described. Recent studies have broadened our understanding of the regulation of anthocyanin synthesis in flowers and fruits, indicating that a regulatory system based on the cooperation of MYB, bHLH and WD40 proteins that control floral and fruit pigmentation is common to many dicot species. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

The biosynthetic pathways of flavonoids and carotenoids have been well established, and the biosynthetic genes have been mostly isolated. Metabolic engineering of their biosynthetic pathways has provided not only novel colored or health-beneficial plants but also excellent models to study the efficacy of such engineering. In order to achieve a specific color by accumulating a corresponding compound, it is necessary to upregulate the pathway leading to the compound and downregulate the competing pathway. The regulation of gene expression has to be optimized in a target crop as well.

Betalains are the yellow and violet pigments that substitute anthocyanins in plants belonging to the order Caryophyllales. These pigments have attracted much attention because of their bioactivities, which range from an antioxidant capacity to the chemoprevention of cancer. However, the biosynthetic pathway of betalains remains under discussion; the main steps have been characterized in recent years, but multiple side reactions are possible. The key enzymes involved have only recently been described, providing clues about the regulation of betalain biosynthesis. In this review, we provide a comprehensive view of the biosynthetic scheme of betalains and discuss the different reactions that have been demonstrated experimentally or proposed in the literature. Copyright © 2013 Elsevier Ltd. All rights reserved.