Integrated transcriptomic and metabolomic analyses reveal the molecular mechanism of flower color differentiation in Orychophragmus violaceus

Yubin Shi ^* Zixuan Wang ^* Zhuangzhuang Yan ^* Jianfeng Liu Jun Zhang ^* Guixia Liu ^*

• College of Life Sciences, Hebei University, Baoding, Hebei Province, China

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