Fig 1.
Testing the influence of different stress conditions on mtDNA transmission in hybrids.
(A) S. cerevisiae and S. paradoxus were refreshed on an YPD agar plate at 28°C overnight before mating experiments. S. cerevisiae and S. paradoxus were crossed and incubated for 3 hours at 28°C to form diploid hybrid cells. Hybrids were picked under a dissecting microscope and immediately cultured under different conditions (2% glucose, 5% glucose, glycerol, osmotic pressure, and ubiquitination inhibition). (B) After these hybrids formed colonies on the solid agar plate, all hybrid cells were grown in liquid medium under the respective conditions, and growth was maintained with daily serial transfers (1:1000 dilution). The mtDNA genotypes were identified after approximate 110 generations according to the digestion at the polymorphic sites of COX3 with the restriction enzymes.
Table 1.
Effects of environmental factors on mitochondrial DNA inheritance in hybrids produced by crossing S. cerevisiae strain W303 with S. paradoxus strain YDG 197.
Table 2.
Effects of environmental factors on mitochondrial DNA inheritance in hybrids produced by crossing S. cerevisiae strain UWOPS83-787.3 with S. paradoxus strain N-17.
Fig 2.
Two possible hypotheses can explain biased mtDNA transmission in yeast hybrids.
(A) Fitness differences exist between the hybrids carrying different mtDNA genotypes. After competition, the cells with higher fitness become dominant. (B) Stress influences mtDNA transmission during budding of progeny directly. Under stress, mtDNA transmission to progeny is biased toward one type of mtDNA genotype.
Table 3.
Summary of the results of fitness competition assay and mtDNA inheritance experiments in Tables 1 and 2.
Fig 3.
Mitochondrial activity of hybrid cells carrying different mtDNA genotypes cultured in 5% glucose, non-fermentable carbon source glycerol-based medium, 0.5 M NaCl to alter osmotic pressure, and 100 mM NH4Cl to inhibit ubiquitination, respectively.
(A) Under the 5% glucose condition, the results showed higher mitochondrial activity in the hybrids carrying S. cerevisiae mtDNA than in those carrying S. paradoxus mtDNA that were produced by crossing strain W303 with strain YDG 197. However, mitochondrial activity did not significantly differ between the hybrids carrying different mtDNA genotypes produced by crossing UWOPS83-787.3 with N-17. (B) Under the glycerol-based condition, the results showed higher mitochondrial activity in the hybrids carrying S. cerevisiae mtDNA than in those carrying S. paradoxus mtDNA that were produced by crossing strain UWOPS83-787.3 with strain N-17. However, mitochondrial activity did not significantly differ between the hybrids carrying different mtDNA genotypes produced by crossing W303 with YDG 197. (C-D) According to the results, neither NaCl nor NH4Cl influence mitochondrial activity in hybrids carrying different mtDNA genotypes. Values represent the mean ± SD for nine biological replicates. Two-tailed t tests were performed using Past Statistics, version 3.12. P < 0.05 was considered statistically significant. *P < 0.05; **P < 0.01.