Fruit Colour and Novel Mechanisms of Genetic Regulation of Pigment Production in Tomato Fruits

Fruit colour represents a genetic trait with ecological and nutritional value. Plants mainly use colour to attract animals and favour seed dispersion. Thus, in many species, fruit colour coevolved with frugivories and their preferences. Environmental factors, however, represented other adaptive forces and further diversification was driven by domestication. All these factors cooperated in the evolution of tomato fruit, one of the most important in human nutrition. Tomato phylogenetic history showed two main steps in colour evolution: the change from green-chlorophyll to red-carotenoid pericarp, and the loss of the anthocyanic pigmentation. These events likely occurred with the onset of domestication. Then spontaneous mutations repeatedly occurred in carotenoid and phenylpropanoid pathways, leading to colour variants which often were propagated. Introgression breeding further enriched the panel of pigmentation patterns. In recent decades, the genetic determinants underneath tomato colours were identified. Novel evidence indicates that key regulatory and biosynthetic genes undergo mechanisms of gene expression regulation that are much more complex than what was imagined before: post-transcriptional mechanisms, with RNA splicing among the most common, indeed play crucial roles to fine-tune the expression of this trait in fruits and offer new substrate for the rise of genetic variables, thus providing further evolutionary flexibility to the character.