The wild allotetraploid sesame genome provides novel insights into evolution and lignan biosynthesis.

introductionThe wild tetraploid sesame (Sesamum schinzianum), an ancestral relative of diploid cultivated sesame, grows in the tropical desert of the African Plateau. As a valuable seed resource, wild sesame has several advantageous traits, such as strong environmental adaptability and an extremely high content of sesamolin in its seeds. High-quality genome assembly is essential for a detailed understanding of genome structure, genome evolution and crop improvement.

objectivesHere, we generated two high-quality chromosome-scale genomes from S. schinzianum and a cultivated diploid elite sesame (Sesamum indicum L.) to investigate the potential genetic basis underlying these traits of wild sesame.

methodsThe long-read data from PacBio Sequel II platform and high-throughput chromosome conformation capture (Hi-C) data were used to construct high-quality sesame genome. Then dissecting the molecular mechanisms of sesame evolution and lignan biosynthesis through comparative genomics and transcriptomics.

resultsWe found evidence of divergent evolution that involved differences in the number, sequence and expression level of homologous genes between the two sets of subgenomes from allotetraploids in S. schinzianum, all of which might be driven by subfunctionalization after polyploidization. Furthermore, it was found that a great number of genes involved in the stress response have undergone positive selection and resulted from gene family expansion in the wild sesame genome compared with the cultivated sesame genome, which, overall, is associated with adaptative evolution to the environment. We hypothesized that the sole functional member CYP92B14 (SscC22g35272) could be associated with high content of sesamolin in wild sesame seeds.

conclusionThis study provides high-quality wild allotetraploid sesame and cultivated sesame genomes, reveals evolutionary features of the allotetraploid genome and provides novel insights into lignan synthesis pathways. Meanwhile, the wild sesame genome will be an important resource to conduct comparative genomic and evolutionary studies and plant improvement programmes.