Elucidation of the key flavonol biosynthetic pathway in golden <i>Camellia</i> and its application in genetic modification of tomato fruit metabolism

Golden <i>Camellia</i> refers to a group of species in the genus <i>Camellia</i> that display yellow petals. The secondary metabolites in these petals hold ornamental significance and potential health benefits. However, the biosynthetic mechanisms governing the synthesis of these metabolites in golden petals remain elusive, and the exploitation of their bioactive components is not fully realized. This research involved the collection and analysis of 23 species of golden <i>Camellia</i>, leading to the discovery that flavonols, particularly quercetin 3-<i>O</i>-glucoside and quercetin 7-<i>O</i>-glucoside, are the primary contributors to the golden flower pigmentation. Integrative transcriptomics and coexpression network analyses pinpointed <i>CnFLS1</i> as a crucial gene in the biosynthetic pathway, which, in conjunction with <i>CnCHS</i>, <i>CnF3'H</i>, and <i>CnUFGT</i>, orchestrates the specific pathway for flower color development. The enzyme assays revealed a high affinity and catalytic efficiency of CnFLS1 for DHQ, and transient expression of <i>CnFLS1</i> in tobacco was shown to enhance the biosynthesis of quercetin flavonols, highlighting the pathway specificity in golden <i>Camellia</i>. Moreover, strategic transformations of cultivated tomatoes with various biosynthetic genes yielded transgenic lines exhibiting yellow fruit and quercetin-enriched flesh. These modified lines not only contained distinct flavonol components characteristic of golden <i>Camellia</i> but also demonstrated markedly improved antioxidant capabilities and enhanced resistance. The outcomes of this study not only elucidate the metabolic processes underlying the pigmentation of golden <i>Camellia</i> flowers but also provide a foundation for the development of novel tomato breeds through synthetic biology.