Complete organelle genomes of Sinapis arvensis and their evolutionary implications

Sinapis arvensis, belonging to the genus Sinapis of the family Brassicaceae, has good agronomic characters that make it a valuable genetic resource for crop improvement and is a cytoplasmic source of heterologous cytoplasmic male sterility (CMS). In addition, S. arvensis has played an important role in the evolution of the six major cultivated Brassica species involved in the triangle of U. Using next-generation sequencing, we assembled and revealed the gene composition of S. arvensis cytoplasmic genome. The chloroplast genome comprises 153,590 bp, with 112 individual genes, including 4 rRNA, 29 tRNA, and 79 protein-coding genes. The mitochondrial genome comprises 240,024 bp, with 54 genes, including 18 tRNA, three rRNA and 33 protein-coding genes. Genome structure and evolutionary analysis indicated that the sequences of the S. arvensis organellar genomes were more similar to those of Brassica nigra and B. carinata than to those of other Brassicaceae species. Four mitochondrial open reading frames displaying chimeric structural features and encoding hypothetical proteins with transmembrane domains may account for the infertility of Nsa CMS previously derived from somatic cell hybridization between B. napus and S. arvensis. These results will not only contribute to utilize the germplasm resource of S. arvensis, and comprehend the evolution of organelle genomes within the Brassicaceae family, but also help to identify genes conditioning the alloplasmic male sterility of Nsa CMS in B. napus.