Characterization of Vicia faba mitochondrial genomes with normal coxII and coxII-orf 192 chimeric genes

Abstract

Southern hybridization analysis of mitochondrial genomes from different lines and cultivars of Vicia faba, with respect to variability of the coxII gene sequence, revealed two predominant types of mitochondrial genomes. The type I mitochondrial genome contained the coxII gene sequence in a 6.5-kb BamHI fragment. Type II had two copies of the coxII sequence: the first in a 6.5-kb and the second in a 2.6-kb BamHI fragment. The second copy was represented by a coxII-orf192 chimeric gene. We found several pure lines with type I and type II mitochondrial genomes. Each type of genome was stably inherited. No chimeric gene was found in mitochondria of the male-sterile line cms447. Nucleotide sequences of Vicia faba mitochondrial DNA (mtDNA) containing normal and chimeric coxII genes are presented. The sequence of the normal coxII gene was compared to the coxII gene from mitochondria of Pisum sativum. The similarity of nucleotide sequences and of predicted amino acid sequences between these two genes was more than 98%. A very high similarity between transcription initiation and termination signals was also observed. The sequence of the chimeric gene was characterized at the 5' end by the almost complete sequence of the normal coxII gene, up to the fifth nucleotide before the termination codon. The 3' end of the chimeric gene was represented by the 3' part of an orf previously called orf128+. The full size of this orf was 576 nucleotides, and the full size of the predicted polypeptide was 192 amino acid residues. Therefore, this orf can be finally called orf192. Northern hybridization analysis showed that orf192 was actively transcribed into a 1.4-kb transcript. The chimeric gene was also transcribed into a minor transcript of about 3 kb. Comparative analysis of the normal coxII gene and orf192 supported the suggestion that the chimeric gene resulted from nonhomologous recombination.