Gene controlled selection of mitochondria in Paramecium

The slow growing mutant cl1 of Paramecium, previously described (Sainsard, Claisse and Balmefrezol, 1974) differs from wild-type by a single recessive nuclear mutation and by a particular mitonchondrial phenotype (Mcl) that gene cl1 distinguishes from the wild-type mitochondrial phenotype (M+). A further analysis of these nucleo-mitochondrial interactions was carried out by confronting the genes cl1 and cl)+ with mixed populations of M+ and Mcl mitochondria obtained after cytoplasmic exchange at conjugation. The following results were obtained: 1. M+ and Mcl mitochondria introduced respectively into mutant and wild-type cells do not multiply easily; 2. when a mixed population (M+ + Mcl) is established, both mitochondrial types are maintained during the growth of the F1 heterozygous cl1/cl1+ clones; 3. when the nuclear segregation occurs in F2, the formation of homozygotes cl1/cl1 or cl1+/cl1+ is soon followed by the segregation of the two mitochondrial types, Mcl or M+, reconstituting the two parental nucleo-mitochondrial associations.