De novo assembly of the complete organelle genome sequences of azuki bean (Vigna angularis) using next-generation sequencers.

Since chloroplasts and mitochondria are maternally inherited and have unique features in evolution, DNA sequences of those organelle genomes have been broadly used in phylogenetic studies. Thanks to recent progress in next-generation sequencer (NGS) technology, whole-genome sequencing can be easily performed. Here, using NGS data generated by Roche GS Titanium and Illumina Hiseq 2000, we performed a hybrid assembly of organelle genome sequences of Vigna angularis (azuki bean). Both the mitochondrial genome (mtDNA) and the chloroplast genome (cpDNA) of V. angularis have very similar size and gene content to those of V. radiata (mungbean). However, in structure, mtDNA sequences have undergone many recombination events after divergence from the common ancestor of V. angularis and V. radiata, whereas cpDNAs are almost identical between the two. The stability of cpDNAs and the variability of mtDNAs was further confirmed by comparative analysis of Vigna organelles with model plants Lotus japonicus and Arabidopsis thaliana.