The chromosome-level Hemerocallis citrina Borani genome provides new insights into the rutin biosynthesis and the lack of colchicine

Hemerocallis citrina Borani (huang hua cai in Chinese) is an important horticultural crop whose flower buds are widely consumed as a delicious vegetable in Asia. Here we assembled a high-quality reference genome of H. citrina using single-molecule sequencing and Hi-C technologies. The genome assembly was 3.77 Gb and consisted of 3183 contigs with a contig N50 of 2.09 Mb, which were further clustered into 11 pseudochromosomes. A larger portion (3.25 Gb or 86.20%) was annotated as a repetitive content and 54,295 protein-coding genes were annotated in the genome. Genome evolution analysis showed that H. citrina experienced a recent whole-genome duplication (WGD) event at ~15.73 million years ago (Mya), which was the main factor leading to many multiple copies of orthologous genes. We used this reference genome to predict 20 genes involved in the rutin biosynthesis pathway. Moreover, our metabolomics data revealed neither colchicine nor its precursors in H. citrina, challenging the long-standing belief that this alkaloid causes poisoning by the plant. The results of our disruptive research are further substantiated by our genomic finding that H. citrina does not contain any genes involved in colchicine biosynthesis. The high-quality genome lays a solid foundation for genetic research and molecular breeding of H. citrina.