Paternal leakage and heteroplasmy of mitochondrial genomes in Silene vulgaris: evidence from experimental crosses.

The inheritance of mitochondrial genetic (mtDNA) markers in the gynodioecious plant Silene vulgaris was studied using a series of controlled crosses between parents of known mtDNA genotype followed by quantitative PCR assays of offspring genotype. Overall, approximately 2.5% of offspring derived from crosses between individuals that were homoplasmic for different mtDNA marker genotypes showed evidence of paternal leakage. When the source population of the pollen donor was considered, however, population-specific rates of leakage varied significantly around this value, ranging from 10.3% to zero. When leakage did occur, the paternal contribution ranged from 0.5% in some offspring (i.e., biparental inheritance resulting in a low level of heteroplasmy) to 100% in others. Crosses between mothers known to be heteroplasmic for one of the markers and homoplasmic fathers showed that once heteroplasmy enters a maternal lineage it is retained by approximately 17% of offspring in the next generation, but lost from the others. The results are discussed with regard to previous studies of heteroplasmy in open-pollinated natural populations of S. vulgaris and with regard to the potential impact of mitochondrial paternal leakage and heteroplasmy on both the evolution of the mitochondrial genome and the evolution of gynodioecy.