High pigment tomato mutants - more than just lycopene (a review)

Fruit constitutes a major component of our diet, providing fiber, vitamins, minerals, and many phytonutrients that promote good health. Fleshy fruits such as tomatoes already contain high levels of several of these ingredients. Nevertheless, efforts have been invested in increasing and diversifying the content of phytonutrients, such as carotenoids and flavonoids, in tomato fruits. These efforts rely on transgenic approaches, and the use of single-point mutations and/or quantitative trait loci affecting levels of these phytonutrients. The tomato high pigment (hp) mutations are a good example of the latter alternative. Due to their impact on fruit lycopene content, hp mutations were already introgressed into elite tomato germplasm. Interestingly, plants carrying these mutations are also characterized by higher levels of other health-promoting metabolites, such as flavonoids and vitamins. These mutations were initially marked as lesions in structural genes of the carotenoid biosynthetic pathway. However, recent studies have shown that they represent mutations in two regulatory genes active in light signal transduction, also known as photomorphogenesis. This gene-identification has created a conceptual link between photomorphogenesis and biosynthesis of fruit phytonutrients, and suggests that manipulation of the light signal transduction machinery in plants may be an effective approach towards practical manipulation of fruit phytonutrients.