Anthocyanins distribution, transcriptional regulation, epigenetic and post-translational modification in fruits

Plant compounds that are perceived by humans to have color are generally referred to as 'pigments'. Their varied structures and colors have long fascinated chemists and biologists, who have examined their chemical and physical properties, their mode of synthesis, and their physiological and ecological roles. Plant pigments also have a long history of use by humans. The major classes of plant pigments, with the exception of the chlorophylls, are reviewed here. Anthocyanins, a class of flavonoids derived ultimately from phenylalanine, are water-soluble, synthesized in the cytosol, and localized in vacuoles. They provide a wide range of colors ranging from orange/red to violet/blue. In addition to various modifications to their structures, their specific color also depends on co-pigments, metal ions and pH. They are widely distributed in the plant kingdom. The lipid-soluble, yellow-to-red carotenoids, a subclass of terpenoids, are also distributed ubiquitously in plants. They are synthesized in chloroplasts and are essential to the integrity of the photosynthetic apparatus. Betalains, also conferring yellow-to-red colors, are nitrogen-containing water-soluble compounds derived from tyrosine that are found only in a limited number of plant lineages. In contrast to anthocyanins and carotenoids, the biosynthetic pathway of betalains is only partially understood. All three classes of pigments act as visible signals to attract insects, birds and animals for pollination and seed dispersal. They also protect plants from damage caused by UV and visible light.

Anthocyanins are important health-promoting pigments that make a major contribution to the quality of fruits. The biosynthetic pathway leading to anthocyanins is well known and the key regulatory genes controlling the pathway have been isolated in many species. Recently, a considerable amount of new information has been gathered on the developmental and environmental regulation of anthocyanin biosynthesis in fruits, specifically the impact of regulation through light. New discoveries have begun to reveal links between the developmental regulatory network and the specific regulators of anthocyanin biosynthesis during fruit ripening. In this opinion article, a simplified model for the different regulatory networks involved with anthocyanin production in fruit is proposed. Copyright © 2013 Elsevier Ltd. All rights reserved.