More than meets the eye: from carotenoid biosynthesis, to new insights into apocarotenoid signaling

Carotenoids are a class of isoprenoids synthesized almost exclusively in plants involved in a myriad of roles including the provision of flower and fruit pigmentation for the attraction of pollinators and seed dispersing organisms. While carotenoids are essential throughout plant development, they are also extremely important in human diets providing necessary nutrition and aiding in the prevention of various cancers, age-related diseases and macular degeneration. Utilization of multiple plant models systems (i.e. Arabidopsis; maize; and tomato) has provided a comprehensive framework detailing the regulation of carotenogenesis throughout plant development covering all levels of genetic regulation from epigenetic to post-translational modifications. That said, the understanding of how carotenoids self-regulate remains fragmented. Recent reports demonstrate the potential influence of carotenoid-cleavage products (apocarotenoids) as signaling molecules regulating carotenoid biosynthesis in addition to various aspects of plants development (i.e. leaf and root development). This review highlights recent advances in carotenogenic regulation and insights into potential roles of novel apocarotenoids in plants.