Growth and Fruit Quality Responses in Wild-type and OXAtCRY1 Tomatoes under Transgrafting Combinations

Tomato is one of the most important vegetable crops worldwide, valued for its nutritional and nutraceutical properties. To enhance its traits and improve pest resistance, grafting has been widely adopted, gaining popularity due to its multiple agronomic benefits. In parallel, agricultural biotechnology has generated genetically modified plants that serve as models for grafting, in which only one component—the rootstock or the scion—is genetically modified. In plants, the cryptochrome gene family mediates photomorphogenic responses to blue light. However, information on the function of CRY1 in species other than Arabidopsis thaliana is currently lacking. To investigate the role of Arabidopsis cryptochrome 1 in other plant species, transgenic tomato (Solanum lycopersicum) lines overexpressing an AtCRY1:GFP fusion under the control of the CaMV 35S promoter were generated. This study aimed to characterize the physiological and molecular interactions between rootstock and scion in two ´Cuatomatl´ morphotype genotypes (Solanum lycopersicum): a wild-type (WT) line and a transgenic line OXAtCRY1. The transgenic nature of the OXAtCRY1 line was confirmed by its phenotypic response to light: hypocotyl inhibition under blue light, reduced growth in adult plants, and increased anthocyanin and chlorophyll accumulation. Four treatments were evaluated: ungrafted WT, ungrafted OXAtCRY1, WT/OXAtCRY1 (WT rootstock with OXAtCRY1 scion), and OXAtCRY1/WT (OXAtCRY1 rootstock with WT scion). Results showed that ungrafted OXAtCRY1 plants accumulated the highest levels of lycopene, β-carotene, total chlorophyll, chlorophyll a, and chlorophyll b. For fruit quality traits such as firmness and °Brix, both grafted and ungrafted OXAtCRY1 performed best, whereas citric acid content was lower in OXAtCRY1 compared to WT. Interestingly, the WT/OXAtCRY1 graft exhibited higher total phenolic content. In contrast, pH and color index were not significantly affected by genotype or grafting treatment.