Abstract
Anthocyanins represent the major red, purple, and blue pigments in many flowers, fruits, vegetables, and cereals. They are also recognized as important health-promoting components in the human diet with protective effects against many chronic diseases, including cardiovascular diseases, obesity, and cancer. Anthocyanin biosynthesis has been studied extensively, and both biosynthetic and key regulatory genes have been isolated in many plant species. Here, we will provide an overview of recent progress in understanding the anthocyanin biosynthetic pathway in plants, focusing on the transcription factors controlling activation or repression of anthocyanin accumulation in cereals and fruits of different plant species, with special emphasis on the differences in molecular mechanisms between monocot and dicot plants. Recently, new insight into the transcriptional regulation of the anthocyanin biosynthesis, including positive and negative feedback control as well as epigenetic and post-translational regulation of MYB-bHLH-WD40 complexes, has been gained. We will consider how knowledge of regulatory mechanisms has helped to produce anthocyanin-enriched foods through conventional breeding and metabolic engineering. Additionally, we will briefly discuss the biological activities of anthocyanins as components of the human diet and recent findings demonstrating the important health benefits of anthocyanin-rich foods against chronic diseases.
Highlights
Anthocyanin synthesis is one of the most studied biosynthetic pathways in plants
Two tightly linked R2R3-MYB genes, SlANT1 and SlAN2, were considered as the main positive regulators controlling anthocyanin levels in the skin of fruits (Mes et al, 2008; Sapir et al, 2008). Both activated anthocyanin biosynthesis when overexpressed in tomato fruits, leaves, and flowers (Mathews et al, 2003; Schreiber et al, 2012; Meng et al, 2015), but only SlAN2 was shown to act as a positive regulator of anthocyanin synthesis in vegetative tissues under high light or low temperature conditions through the control of the expression of the bHLHs SlAN1 and SlJAF13 (Kiferle et al, 2015)
In order to increase the anthocyanin content in tomato fruits, anthocyanin regulatory genes from different plant species have been expressed in tomato most successfully when the bHLH Delila and MYB Rosea1 genes from snapdragon were overexpressed under the control of a tomato fruit-specific promoter, to give purple tomato fruits containing large amounts of anthocyanins and flavonols both in the peel and flesh (Butelli et al, 2008)
Summary
Anthocyanin synthesis is one of the most studied biosynthetic pathways in plants. Besides providing the major red, purple, violet, and blue pigmentation in flowers and fruits for attracting pollinators and seed dispersers, anthocyanins act as antioxidants in plants and are involved in both abiotic and biotic stresses, such as UV radiation, cold temperatures, drought, and in defense against pathogens and herbivores (Sarma and Sharma, 1999; Lorenc-Kukuła et al, 2005; Gould and Lister, 2006). Ethylene inhibits anthocyanin accumulation induced by sucrose and light by suppressing the expression of transcription factors that positively regulate anthocyanin biosynthesis, including GL3, TT8, and PAP1, while activating the negative regulator MYBL2 (Jeong et al, 2010).
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