Abstract Triticale, an intergeneric hybrid crop-plant, is generated when female wheat lines are fertilised with pol- len from rye. We have investigated the mitochondrial DNA organisation and the expression of a total of 11 different triticale genotypes, varying in their nuclear and cytoplas- mic backgrounds. In Southern hybridisations using probes homologous to the upstream flanking sequences, mtDNA fragments characteristic of both wheat and rye mtDNA can be detected in all triticale lines analysed. In addition, clones isolated fom a triticale lambda library exhibit either a ma- ternal-like or paternal-like organisation of the orf25 gene region. By PCR cloning, four different orf25 gene copies were identified in triticale, three of which correspond to maternal (85%) or paternal (12%) orf25 sequences. Three percent of all clones represent a novel type, that might have arisen by homologous recombination. Although these data suggest biparental inheritance of mtDNA in wheat/rye crosses, paternal-like gene copies can also be detected in maternal wheat mitochondria. Their stoichiometry as as- sayed by competitive PCR is about 0.1% of total orf25 gene copies. The high abundance of paternal-like sequences in the F 1 hybrid might therefore be due to either the transmis- sion of rye mtDNA in the intergeneric cross and/or the am- plification of sequences in triticale that persist in sub-stoi- chiometric amounts in wheat. These data suggest that am- plification and recombination of sub-genomic mitochon- drial molecules are affected by different nuclear genotypes. Interestingly, sequence analysis of triticale RT-PCR clones indicates a selective transcription of maternal-like orf25 gene copies in triticale. Mitochondrial gene expression may therefore possess mechanisms to compensate for the variation of mtDNA organisation. Key words Triticale · Mitochondrial DNA · orf25 gene · Transcriptional expression Introduction It is generally believed that genomes from plastids and from mitochondria are inherited in a maternal fashion in most plants (Whatley 1982; Reboud and Zeyl 1994). Ge- netical and cytological studies, however, have revealed that a biparental inheritance of chloroplasts occurs in some an- giosperms, for example Oenothera, Pelargonium, or Med- icago sativa (Smith et al. 1986; Chiu et al. 1988; Tilney- Bassett et al. 1992). Using epifluorescence microscopic procedures to screen pollen from 235 different angio- sperms, evidence for a potentially paternal transmission of plastid DNA was provided in approximately 20% of the species investigated (Corriveau and Coleman 1988). The application of molecular techniques such as restriction fragment length polymorphism (RFLP) and hybridisation analyses proved that, in contrast to angiosperms, plastids are inherited by the paternal parent in most gymnosperm families (Wagner et al. 1987; Szmidt et al. 1987; Stine et al. 1989; Neale and Sederoff 1989; White 1990). Mitochondrial DNA, however, seems to be maternally inherited even in species which exhibit a paternal trans- mission of chloroplasts (Neale and Sederoff 1989; Sutton et al. 1991; DeVerno et al. 1993). The only exceptions so far with paternal inheritance of both plastid and mitochon- drial DNA have been found in the gymnosperm species Sequoia sempervirens and Calocedrus decurrens (Neale Curr Genet (1997) 32: 337–347 © Springer-Verlag 1997 Received: 5 June 1997 / 20 August 1997 Beate Laser · Sabine Mohr · Werner Odenbach Gitta Oettler · Ulrich Kück Parental and novel copies of the mitochondrial orf25 gene in the hybrid crop-plant triticale: predominant transcriptional expression of the maternal gene copy ORIGINAL PAPER B. Laser 1 · S. Mohr 2 · U. Kück () Lehrstuhl für Allgemeine Botanik, Ruhr-Universität Bochum, D-44780 Bochum, Germany Fax: ++49-234-70 94-1 84 e-mail: ulrich.kueck@ruhr-uni-bochum.de W. Odenbach Institut für Angewandte Genetik, FU Berlin, D-14195 Berlin, Germany G. Oettler Landessaatzuchtanstalt der Universität Hohenheim, D-70593 Stuttgart, Germany Present address: 1 Unité de Diabetologie Clinique, Centre Médical Universitaire, 1, rue Michel Servet, CH-1211 Genève 4, Switzerland 2 Departments of Molecular Genetics and Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA Communicated by A. Brennicke