Integrated transcriptomics and metabolomics analysis to characterize the optimal picking time in yellowhorn (Xanthoceras sorbifolium) flowers

Yellowhorn (Xanthoceras sorbifolium) is a unique species in China and has a very high medicinal value because it contains high levels of flavonids. In production, farmers generally harvest at the early flowering phase, but the flavonoid content is different at the flowering stage. Therefore, the study performed metabolomic and transcriptomic profiling of three flowering phases (early, middle, and full of flowering) to detect quantitative and qualitative changes with respect to the flavonoid accumulation in yellowhorn flowers during their development. For the majority of the yellowhorns, the highest flavonoid content was obtained at the full flowering phase; among the flavonoids, the content of peonidin-3-O-glucoside was the highest. This finding suggests that maximum utilisation value can be achieved and economic benefits can be improved by harvesting the flowers at the full flowering phase rather than the early flowering phase. In addition, the transcriptomic results showed that MYB and WD40 transcription factors were correlated with anthocyanin accumulation. Our findings not only provide a theoretical basis for the regulation mechanism of flavonoid metabolism in yellowhorn petals, but also provide a basis for the industrial production of yellowhorn.