Integrated transcriptomic and metabolomics analysis reveal the molecular mechanism of flower color differentiation of Orychophragmus violaceus

Orychophragmus violaceus has been a popular horticultural plant for its bright purple flower, which is commonly found in parks and green belts. However, three flower colors (purple, light purple, and white) can be seen from the wild types of O. violaceus in nature. The molecular mechanism underlying the intriguing flower colors formation is still unknown. Here, we combined metabolomics and transcriptomics to identify a pathway cascade leading to anthocyanin biosynthesis associated with flower colors formation of O. violaceus. A total of 152 flavonoids metabolites were identified based on metabolomics data, most of which were quercetins and kaempferols. The comparative analysis of metabolites among three flower samples indicates that two anthocyanins, peonidin-3-glucoside and delphinidin 3-(6''-malonyl-glucoside) are the most likely purple pigments responsible for the coloration of petals of O. violaceus. Subsequent transcriptomic analysis showed 5918 differential expressed genes among three groups of flowers, 87 of which encode 13 key enzymes in anthocyanin biosynthetic pathway. Moreover, high expression of two transcription factors OvMYB and OvbHLH in purple flower suggested their role in regulation of anthocyanin biosynthesis. By integrating metabolomic and transcriptomic data, the OvANS encoding an anthocyanidin synthase, responsible for the transformation of colorless leucoanthocyanidin to colored anthocyanidin, is significantly upregulated in purple flower. This study provides novel insights into the molecular mechanism for flower color development for O. violaceus, which lays the foundation for its flower color breeding.