MITOCHONDRIAL GENOME TRANSMISSION IN CHLAMYDOMONAS DIPLOIDS OBTAINED BY SEXUAL CROSSES AND ARTIFICIAL FUSIONS - ROLE OF THE MATING TYPE AND OF A 1 KB INTRON

The linear mitochondrial DNAs of the two infertile algal species Chlamydomonas smithii and C. reinhardtii are co-linear with the exception of a 1 kb intron (α intron) located in the cytochrome b gene of C. smithii. C. smithii also possesses an additional HpaI restriction site (H marker) located in the COXI gene, about 5 kb from the intron. In reciprocal crosses, C. smithii (H+α+) × C. reinhardtii (H-α-), the α intron is transmitted to all diploid progeny, whereas the H marker is frequently transmitted either biparentally or paternally depending on whether the C. smithii parent is maternal (mt+) or paternal (mt-). In diploids resulting from artificial fusion between vegetative cells, the absolute transmission of a is accompanied by the frequent transmission of the H+ marker, irrespective of the mating type of the parental strains. Finally, in reciprocal crosses between C. smithii (H+α+) and recombinant H-α+ clones, the transmission of the H marker is predominantly paternal or biparental. These results allow us to conclude that (1) the a intron behaves as a group I intron whose unidirectional conversion influences the transmission of the H marker; and (2) the mt- paternal mitochondrial genome is transmitted more often than the mt+. The mating type has no effect in diploids obtained by artificial fusion. © 1990 Springer-Verlag.