The Molecular Basis of Genetic Diversity among Cytoplasms of Triticum and Aegilops. VIII. Mitochondrial RFLP Analyses Using Cloned Genes as Probes

Abstract

Restriction fragment length polymorphisms (RFLPs) among mtDNA digests of Triticum and Aegifops species have been analyzed by Southern blot hybridization with four cloned mitochondrial genes as probes. Three Triticum and 14 ( 16 sources, in total) Aegilops species have been studied. These represent the three wheat groups Einkorn, Dinkel, and Timopheevi and all six Aegilops sections (Polyeides, Cylindropyrum, Vertebra@ Sitopsis, Amblyopyrum, and Comopyrum) . Hybridization patterns of eight restriction-enzyme /probe combinations (BumHIor HindIIIdigested mtDNAs probed with four mtDNA clones, each containing one of the four genes atpA, coxll, rrn18&5, or rrn26) were examined. With all of the probes used, mtDNA from one source of Ae. speltoides showed hybridization profiles identical to those of T. timopheevi, and mtDNA from Ae. searsii gave profiles identical to those of Ae. kotschyi. Otherwise, different hybridization profiles were found among all mtDNAs, giving 19 mtDNA samples classifiable into 17 different types. Based on the percentages of common fragments among all pairs of mtDNAs, a phylogenetic tree of mitochondrial genomes was generated by the UPGMA method. The resultant tree showed that the mitochondrial genomes of Triticum and Aegilops have differentiated into three major groups: ( 1) T. monococcum, (2) Ae. speltoides and polyploid wheats, and (3) all other species. The hybridization patterns also revealed differences in copy numbers of all mitochondrial genes, although the extent of polymorphisms differed with the different probes. Stoichiometric fragments of one accession often corresponded to substoichiometric fragments of other accessions, suggesting quantitative, rather than qualitative, differentiation of mitochondrial genomes among accessions.