Genome assembly of the Brassicaceae diploid Orychophragmus violaceus reveals complex whole-genome duplication and evolution of dihydroxy fatty acid metabolism.

Orychophragmus violaceus is a Brassicaceae species widely cultivated in China, particularly as a winter cover crop in northern China because of its low-temperature tolerance and low water demand. Recently, O. violaceus has also been cultivated as a potential industrial oilseed crop because of its abundant 24-carbon dihydroxy fatty acids (diOH-FAs), which contribute to superior high-temperature lubricant properties. In this study, we performed de novo assembly of the O. violaceus genome. Whole-genome synteny analysis of the genomes of its relatives demonstrated that O. violaceus is a diploid that has undergone an extra whole-genome duplication (WGD) after the Brassicaceae-specific α-WGD event, with a basic chromosome number of x = 12. Formation of diOH-FAs is hypothesized to have occurred after the WGD event. Based on the genome and the transcriptome data from multiple stages of seed development, we predicted that OvDGAT1-1 and OvDGAT1-2 are candidate genes for the regulation of diOH-FA storage in O. violaceus seeds. These results may greatly facilitate the development of heat-tolerant and eco-friendly plant-based lubricants using O. violaceus seed oil and improve our understanding of the genomic evolution of Brassicaceae.