Chondriome-type characterization of potato: mt α, β, γδɛ and novel plastid-mitochondrial configurations in somatic hybrids

Abstract

 One hundred and eighty dihaploid clones used for protoplast fusions, and 144 tetraploid German potato cultivars were analysed for their cytoplasms using 11 homologous mt DNA-probes, and were classified as mitochondrial (mt) types α, β, γ, δ, and ɛ according to their RFLP patterns. From the 4x cultivars, 79 had the typical mt-type β of Solanum tuberosum being different from the 46 cvs which had the mt-α type and 19 others with mt-γ. A dendrogram shows their relationships to other Solanum species. The distantly related mt-ɛ was only found in di-haploids, and particularly in clones deriving from Solanum phureja and Solanum andigena. Accessory 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 novel plastid-mitochondrial configurations we have analyzed four representative populations, which derive from different fusion-combination classes: [α (+) β], [α (+) γ], [α (+) δ] and [α (+) ɛ]. On the mitochondrial expression level, hybrids from an [α (+) ɛ] fusion could be distinguished by in-organello translation from [α (+) β] hybrids, and other di-haploids, by an additional translation product of 15 kDa. In fusion parents with mt-α and -γ an additional atp6 reading frame is detectable in sub-stoichiometric amounts by the use of specific 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 characteristic for somatic hybrids was the partial addition of parental mt sub-genomes. The major part of them revealed a new organization in their mt genomes at the mt-type characteristic loci rpl5, rps14, cob, rps10, coxI and rpl2, which contain recombination-specific repeats homologous to Petunia spp. and Nicotiana. A schematic model for the formation of novel mitochondrial genomes in potato somatic hybrids is provided.