Beyond green and red: unlocking the genetic orchestration of tomato fruit color and pigmentation

Fruit color is a genetic trait and a key factor for consumer acceptability and is therefore receiving increasing importance in several breeding programs. Plant pigments offer plants with a variety of colored organs that attract animals for pollination, favoring seed dispersers and conservation of species. The pigments inside plant cells not only play a light-harvesting role but also provide protection against light damage and exhibit nutritional and ecological value for health and visual pleasure in humans. Tomato (Solanum lycopersicum) is a leading vegetable crop; its fruit color formation is associated with the accumulation of several natural pigments, which include carotenoids in the pericarp, flavonoids in the peel, as well as the breakdown of chlorophyll during fruit ripening. To improve tomato fruit quality, several techniques, such as genetic engineering and genome editing, have been used to alter fruit color and regulate the accumulation of secondary metabolites in related pathways. Recently, clustered regularly interspaced short palindromic repeat (CRISPR)-based systems have been extensively used for genome editing in many crops, including tomatoes, and promising results have been achieved using modified CRISPR systems, including CAS9 (CRISPR/CRISPR-associated-protein) and CRISPR/Cas12a systems. These advanced tools in biotechnology and whole genome sequencing of various tomato species will certainly advance the breeding of tomato fruit color with a high degree of precision. Here, we attempt to summarize the current advancement and effective application of genetic engineering techniques that provide further flexibility for fruit color formation. Furthermore, we have also discussed the challenges and opportunities of genetic engineering and genome editing to improve tomato fruit color.