A high frequency of intergenomic mitochondrial recombination and an overall biased segregation of Brassica campestris or recombined Brassica campestris mitochondria were found in somatic hybrids made within Brassicaceae

Mitochondrial segregation and rearrangements were studied in regenerated somatic hybrids from seven different species combinations produced using reproducible and uniform methods. The interspecific hybridizations were made between closely or more distantly related species within the Brassicaceae and were exemplified by 3 intrageneric, 2 intergeneric and 2 intertribal species combinations. The intrageneric combinations were represented by Brassica campestris, Brassica oleracea, Brassica napus, Brassica nigra and Brassica napus, Brassica juncea (tournefortii) hybrids, the intergeneric combinations by B. napus, Raphanus sativus and B. napus, Eruca sativa hybrids, and the intertribal combinations by B. napus, Thlaspi perfoliatum and B. napus, Arabidopsis thaliana hybrids. In each species combination, one of the two mitochondrial genotypes was B. campestris since the B. napus cultivar used in the fusions contained this cytoplasm. Mitochondrial DNA (mtDNA) analyses were performed using DNA hybridization with nine different mitochondrial genes as probes. Among the various species combinations, 43-95% of the hybrids demonstrated mtDNA rearrangements. All examined B. campestris mtDNA regions could undergo intergenomic recombination since hybrid-specific fragments were found for all of the mtDNA probes analysed. Furthermore, hybrids with identical hybridspecific fragments were found for all probes except cox2 and rrn18/rrn5, supporting the suggestion that intergenomic recombination can involve specific sequences. A strong bias of hybrids having new atpA- or atp9-associated fragments observed in the intra-and intergeneric combinations could imply that these regions contain sequences that have a high reiteration number.