Identification and characterization of abundant repetitive sequences in Allium cepa.

Species of the genus Allium are well known for their large genomes. Allium cepa is of great economic significance. Among vegetables, it ranks second after tomato in terms of the global production value. However, there is limited genomics information available on A. cepa. In this study, we sequenced the A. cepa genome at low-coverage and annotated repetitive sequences by using a combination of next-generation sequencing (NGS) and bioinformatics tools. Nearly 92% of 16 Gb haploid onion genome were defined as repetitive sequences, organized in 162 clusters of at least 0.01 percent of the genome. Of these, a proportion representing 40.5% of the genome were further analyzed in detail to obtain an overview of representative repetitive elements present in the A. cepa genome. Few representative satellite repeats were studied by fluorescence in situ hybridization (FISH) and southern blotting. These results provided a basis for evolutionary cytogenomics within the Allium genus.