Carotenoid fortification of zucchini fruits using a viral RNA vector

Background Carotenoids are health‐promoting metabolites in livestock and human diets. Some important crops have been genetically modified to increase their content. Although the usefulness of transgenic plants to alleviate nutritional deficiencies is obvious, their social acceptance has been controversial. Results Here, we demonstrate an alternative biotechnological strategy for carotenoid fortification of edible fruits in which no transgenic DNA is involved. A viral RNA vector derived from zucchini yellow mosaic virus (ZYMV) was modified to express a bacterial phytoene synthase (crtB), and inoculated to zucchini (Cucurbita pepo L.) leaves nurturing pollinated flowers. After the viral vector moved to the developing fruit and expressed crtB, the rind and flesh of the fruits developed yellow‐orange rather than green color. Metabolite analyses showed a substantial enrichment in health‐promoting carotenoids, such as α‐ and β‐carotene (provitamin A), lutein and phytoene, in both rind and flesh. Conclusion Although this strategy is perhaps not free from controversy due to the use of genetically modified viral RNA, our work does demonstrate the possibility of metabolically fortifying edible fruits using an approach in which no transgenes are involved. Graphical and Lay Summary Inoculation of zucchini plants with a zucchini yellow mosaic virus (ZYMV) vector that expresses a bacterial phytoene synthase (crtB) induces yellow‐orange fruits that accumulate health‐promoting carotenoids. This is an alternative strategy for metabolic fortification of edible fruits that avoids labor‐intensive and time‐consuming approaches based on breeding or plant transformation.