Repetitive Sequences in Sesame Genome

Repetitive DNA sequences are the homologous DNA fragments with multiple copies and are the main components in higher plant genomes. Reliable chromosome-scaled genome assembly provided abundant genome information regarding genome structure research in sesame. In this chapter, we present the genome structure character and distribution of interspersed repeat sequences and the tandem repeats in the assembled genome of sesame var. Yuzhi 11 (version 3.0). For S. indicum, the content of interspersed repeat sequences is 46.11%. Of the five groups of interspersed repetitive sequences, i.e., SINEs, LINEs, long terminal repeat (LTR) element, DNA element, and unknown dispersed repeat elements, LTR group is the biggest known repeat type and occupies 11.41% of the assembled genome (335 Mb). Ty1-Copia is the major superfamily in LTR-RTs. In sesame genome, distribution of the tandem repeats, such as rDNA, telomere, and centromere repeats, reflects the character of species. Cytogenetic analyses and genome structure showed that the individual 26 chromosomes in S. indicum have telomeric repeats at the terminal position. The telomeres of sesame are conserved, and the repeat sequences are same with the common repeat unit of TTTAGGG. A total of 1235 telomeric repeat of (TTTAGGG)3 were found in the assembled genome. Meanwhile, about three thousand 45S and 5S rDNA repeats are detected in the assemble genome, which accord with the rDNA content range in other plants. Distribution characters and copy number of telomeres and rDNAs reflect the relative completeness of the assembled sesame genome. In addition, distribution of simple sequence repeats (SSRs) in sesame genome also has been precisely analyzed. A 153 bp centromeric repeat sequence is identified in sesame genome for the first time, which supplies more information for exploring the genome evolution of Sesamum.