Chromosome-scale genome assembly of marigold (Tagetes erecta L.): An ornamental plant and feedstock for industrial lutein production

Marigold (Tagetes erecta L., African marigold) is a widely grown ornamental plant and a main source of the carotenoid lutein for the industrial production of pharmaceuticals, food coloring, and feed additives. To gain a deeper understanding of the genetic mechanism of lutein in marigold, a chromosome-scale assembly of the marigold (T. erecta V-01) genome was completed based on Illumina, PacBio, and Hi-C reads. The 707.21-Mb assembled genome consisted of 35 834 annotated protein-coding genes, with 97.7% genomic integrity. We anchored 87.8% of the contigs (covering 621.20 Mb) to 12 pseudochromosomes, bringing the scaffold N50 length to 54.15 Mb. Phylogenetic analysis showed that marigold was closely related to the Asteraceae species bitter vine (Mikania micrantha) and sunflower (Helianthus annuus), all three of which originated in the Americas. Marigold diverged from the sunflower clade 23.57 million years ago (MYA) and from M. micrantha 19.59 MYA. Marigold has undergone three whole-genome duplication events, as well as a recent whole-genome duplication event (WGD-2) common to H. annuus and M. micrantha. Marigold gene families were significantly less expanded than those of M. micrantha or H. annuus, and the marigold genome contained significantly fewer interspersed repeats, which might account for its smaller genome. In addition, a range of candidate genes involved in the lutein biosynthetic pathway were identified. The high-quality reference genome obtained in this study provided a valuable genomic resource for studying the evolution of the Asteraceae family and for improving marigold breeding strategies.