Lethal mitochondrial genotypes in Podospora anserina: A model for senescence

Summary Crosses between spg1 and spg2, two mitochondrial mutants of Podospora anserina, yield a new type of strain, called pseudo wild-type (PSW), in addition to wild-type recombinants. PSW strains are characterized by a variable phenotype for germination of ascospores and a variable longevity. By autofecondation, PSW strains yield early lethal strains (which die soon after the germination of the spores and so cannot be used for further studies), short-lived strains (which stop their vegetative growth after several centimeters) and long-lived strains (which grow longer than 16 cm). Genetic analysis of the last two categories shows that the PSW phenotype corresponds to a new mitochondrial genotype resulting from the interaction of the two parental mitochondrial genomes.Variability in the longevity of PSW strains is interpretated as the result of a high rate of mutation of their mitochondrial genome into a lethal and suppressive genome, similar to that of the mitochondrial rho ^- suppressive mutant of yeast. Furthermore, on the basis of the striking similarities observed between short-lived PSW strains and senescent cultures of Podospora anserina, we propose that commitment and development of senescence in wild-type strains of Podospora anserina would result, in a similar way, of spontaneous suppressive rho ^--like mitochondrial mutations.