Huang, H.-Q., Liu, J.-D., Duan, J.-Q., Liang, X.-N. and Liu, F.-H. 2012. Cloning and characterization of the mitochondrial genesCox II and atpA from ramie (Boehmeria nivea (L.)Gaud.) and their possible role in cytoplasmic male sterility. Can. J. Plant Sci. 92: 1295-1304. In plants, cytoplasmic male sterility (CMS) is known to be associated with structural changes and the presence of new chimeric genes in mtDNA. In this study, fragments of the Cox II and atpA genes, cloned from mtDNA of three lines (CMS line, its maintainer and restorer lines) of ramie [Boehmeria nivea (L.) Gaud.], showed homology of 95% for Cox II and 97% for atpA compared with the reference dicotyledons in GenBank. The whole sequences of these two genes were obtained using the DNA walking strategy. Cox II showed no difference among the three lines in sequences of DNA and deduced amino acids. However, atpA from the CMS line obviously differed from that of fertile lines in DNA sequence, amino acid sequence and secondary structure of the predicted protein. Unusually low expression was revealed via RT-PCR for atpA in the CMS line at the budding and late-bloom stages. In conclusion, the variation in DNA sequence and the encoded product, and/or the abnormal expression of atpA in the CMS line, may cause male sterility in ramie.