Roles Of Epigenetic Variation In Phenotypic Responses Of Hydrocotyle Vulgaris To Environmental Changes

Heritable epigenetic modifications may occur in response to environmental variation,further altering phenotypes through gene regulation,without genome sequence changes.Thus,it may provide a rapid pathway for plants to adapt to novel and changing environments.However,studies on ecological epigenetics of clonal plants are still scarce.In this study,Hydrocotyle vulgaris,an exotic clonal plant species that widely distributes in wetlands,was used as the model system.By using the theories and methods of experimental ecology and molecular ecology,this study investigated genetic variation and epigenetic variation in natural populations,the relationship between phenotypic variation and epigenetic variation when plants respond to environmental changes,and the heritability of epigenetic modification and its contribution to parental effects.The main results are as follows:1.The populations of H.vulgaris exhibited extremely low genetic diversity,but significantly higher epigenetic diversity.Intra-population genetic diversity was related to epigenetic diversity,and inter-population epigenetic distance was marginally positively correlated with genetic distance.There was no significant relationship between intra-/inter-population genetic variation and phenotypic variation.When genetic variation was controlled,intra-population epigenetic diversity was related to petiole length,leaf area,and specific leaf area variation,while inter-population epigenetic distance was related to leaf area differentiation.The results suggest that even though epigenetic variation is partly under genetic control,it also can independently play a potential role in shaping phenotypes of natural clonal plant populations.2.Artificially-constructed H.vulgaris populations were exposed to two manipulated flood regimes(submergence vs.semi-submergence)to test the role of DNA methylation in regulating phenotypic responses to changing environments.There were different phenotypes and significant epigenetic differentiation between semi-submerged and submerged populations with the same genotype.Moreover,population were under selection.Some phenotypic variation was associated with environment-induced DNA methylation variation,and different subepiloci were functionally close to different traits.Therefore,DNA methylation can play a pivotal role in plant response to stress and ecological adaptation,independent of genetic variation.3.To test the role of epigenetic variation in parental effects,parental generation of H.vulgaris was subjected to two levels of light intensity(light vs.shade)crossed with two levels of DNA demethylation(with vs.without Zebularine),and then offspring taken from each of the four types of parent plants were subjected to the same two light levels(light vs.shade).In parental generation,application of demethylating agent Zebularine enhanced DNA methylation changes.Parental effects tended to exist under shade condition,and non-demethylated parents transmitted 94.44%DNA methylation changes to their offspring,indicating that heritable DNA methylation variation is the potential mechanism of parental effects.Moreover,offspring can remember the methylation state of their parents and reprogram to adapt to the new environment.Alltogether,the results indicate that environment-induced epigenetic variation plays an important role in phenotypic responses and ecological adaptation of the clonal plant H.vulgaris,independent of genetic variation,providing a rapid way to enhance evolutionary potential of plants.This study will help us understand the influence of epigenetic variation on the evolutionary potential of clonal plants,and contribute to the development of theories of evolutionary ecology and ecological epigenetics.