Chondriome-type characterization of potato: mt alpha, beta, gamma, delta, epsilon and novel plastid-mitochondrial configurations in somatic hybrids

One hundred and eighty dihaploid clones used for protoplast fusions, and 14 4 tetraploid German potato cultivars were analysed for their cytoplasms usi ng II homologous mt DNA-probes, and were classified as mitochondrial (mt) t ypes alpha, beta, gamma, delta, and epsilon according to their RFLP pattern s. From the 4x cultivars, 79 had the typical mt-type beta of Solanum tubero sum being different from the 46 cvs which had the mt-cn type and 19 others with mt-gamma. A dendrogram shows their relationships to other Solanum spec ies. The distantly related mt-e was only found in di-haploids, and particul arly in clones deriving from Solanum phureja and Solanum andigena. Accessor y mt types will be actualized on website (http://www.edv.agrar.tu-muenchen. de/pbpz/ mm/mt/al1.htm). In order to evaluate the genetic potential of nove l plastid-mitochondrial configurations we have analyzed four representative populations, which derive from different fusion-combination classes: [alph a (+) beta], [alpha (+) gamma], [alpha (+) delta] and [alpha (+) epsilon]. On the mitochondrial expression level, hybrids from an [alpha (+) epsilon] fusion could be distinguished by in-organello translation from [alpha (+) b eta] hybrids, and other di-haploids, by an additional translation product o f 15 kDa. In fusion parents with mt-alpha and -gamma an additional atp6 rea ding frame is detectable in sub-stoichiometric amounts by the use of specif ic PCR primers. The gene differs from the original 211 bp 3' from the stop codon. Novel RFLP-patterns in 10% of the somatic hybrids were due to a high -rate replication of this pre-existing parental genome region. A second cha racteristic for somatic hybrids was the partial addition of parental mt sub -genomes. The major part of them revealed a new organization in their mt ge nomes at the mt-type characteristic loci rpl5, rps14, cob, rps10, coxI and rpl2, which contain recombination-specific repeats homologous to Petunia sp p. and Nicotiana. A schematic model for the formation of novel mitochondria l genomes in potato somatic hybrids is provided.