Characterization of the complete chloroplast genome sequence and phylogenetic analysis of B. oleracea var. italica

Abstract

Backgrounds: Broccoli (Brassica. oleracea var. italica L.) is known as one of the most nutritionally rich vegetables, as well as rich in functional components that benefit to health. The main purposes of this research were sequencing, assembling and annotation of chloroplast genome of broccoli based on Illumina HiSeq2500 sequencing platform. Results: The size of the broccoli cp genome is 153,364 bp, including two inverted repeat (IR) regions of 26,197 bp each, separated by a small single copy (SSC) region of 17,834 bp and a large single copy (LSC) region of 83,136 bp. The GC content of the complete genome is 36.36%, while those of SSC, LSC, and IR are 29.1%, 34.15% and 42.35%, respectively. It harbors 134 functional genes, including 87 protein-coding genes, 39 tRNAs and 8 rRNAs, with 31 duplicates in the IRs. The most abundant amino acid in the protein-coding genes is leucine, while the least is cysteine. Codon usage frequency showed bias for A/T-ending codons in the cp genome. In the repeat structure analysis, a total of 34 repeat sequences and 291 simple sequence repeat (SSRs) were detected in the work. Although cp genomic structure and size are highly conserved, the SC-IR boundary regions are variable between the 7 cp genomes. The phylogenetic relationships based on complete cp genome from 9 species suggest that B. oleracea var. italica is closely related to Brassica juncea. Conclusions: The complete cp genome sequence was obtained and annotated for broccoli for the first time. The information acquired from this research will be useful for further species identification, population genetics and biological research of broccoli.