Dark side of anthocyanin pigmentation

Dark pigmentation can be observed in various parts of the plant, ranging from foliage to petals and berries. Here, we review the available knowledge about dark pigmentation in plants and the potential for biotechnological applications. The molecular basis of black pigmentation appears to vary among species, with anthocyanins playing a significant role, although specific anthocyanin types and their mechanisms differ. These findings suggest that the development of phenotypes is species-specific or varies between larger taxonomic groups; this is further supported by the polyphyletic nature of dark pigmentation. Additionally, several different regulatory mechanisms have been described for the occurrence of dark pigmentation. First, the repression or knockout of the competing flavone biosynthesis has been shown to lead to darker pigmentation while another mechanism is based on the activation and upregulation of the anthocyanin biosynthesis genes in the presence of MYB transcription factors. Potential ecological functions of dark pigmentation were identified as protection of the photosynthesis apparatus, camouflage against herbivores, and the attraction of pollinators. Promising industrial applications include microbial factories for the production of natural food colourants, induction of novel phenotypes for the ornamental plant industry and, lastly, increase of anthocyanins within agriculturally relevant crops. Understanding the genetic basis of dark pigment accumulation would facilitate biotechnological and agricultural applications.