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 regenerat ed somatic hybrids from seven different species combinations produced using reproducible and uniform methods. The interspecific hybridizatio ns were made between closely or more distantly related species within the Brassicaceae and were exemplified by three intrageneric, two inter generic and two intertribal species combinations. The intrageneric com binations were represented by Brassica campestris (+) B. oleracea, B. napus (+) B. nigra and B. napus (+) B. 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 hy brids. In each species combination, one of the two mitochondrial genot ypes was B. campestris since the B. napus cultivar used in the fusions contained this cytoplasm. Mitochondrial DNA (mtDNA) analyses were per formed using DNA hybridization with nine different mitochondrial genes as probes. Among the various species combinations, 43-95% of the hybr ids demonstrated mtDNA rearrangements. All examined B. campestris mtDN A regions could undergo intergenomic recombination since hybrid-specif ic fragments were found for all of the mtDNA probes analysed. Furtherm ore, hybrids with identical hybrid-specific fragments were found for a ll probes except coxII and rrn18/rrn5, supporting the suggestion that intergenomic recombination can involve specific sequences. A strong bi as of hybrids having new atpA- or atp9-associated fragments observed i n the intra- and intergeneric combinations could imply that these regi ons contain sequences that have a high reiteration number, which gives them a higher probability of recombining. A biased segregation of B. campestris-or B. campestris-like mitochondria was found in all combina tions. A different degree of phylogenetic relatedness between the fusi on partners did not have a significant influence on mitochondrial segr egation in the hybrids in this study.