Meeting Abstract
While mitochondrial (mt) genes in bilaterian animals have high mutation rates, mt genomes in most angiosperms evolve slowly. However, in the angiosperm genus Silene, some species show mammalian-like (“fast”) patterns while closely related species show more typical “slow” rates. This allows us to investigate whether mt function is maintained in “fast” lineages via either: 1) nuclear mutations that compensate for rapidly accumulating, possibly deleterious mt mutations or 2) through strong purifying selection on mt mutations. In this experiment, we compare mt respiration in “fast” species to “slow” species to determine the effect of the many nonsynonymous mt changes that have accumulated in “fast” species. Mt respiration was measured from isolated leaf mitochondria using a new protocol for the Oroboros O2k system. Flux control factors for seven unique respiratory states were calculated to examine the contribution of specific OXPHOS enzymes to respiration (e.g., CI vs. CII). Preliminary results indicate few significant differences in mt function between “fast” and “slow” species. To determine if complementary nuclear changes are responsible for maintaining mt function, respiration was quantified in F2 paternal backcrossed hybrids between two “fast” species, intended to moderately breakup coadapted mitonuclear genotypes. Although germination rates were low in the F2 plants, mt respiration was generally similar to the parental species, with chimeric OXPHOS complexes showing the same or even elevated flux in the hybrids. Together, these results suggest mt purifying selection may be the dominant evolutionary force acting to maintain mt function in “fast” Silene. However, nuclear compensation could still play a role. Future research should explore other fast-evolving angiosperm lineages.
