Epigenetic Variations Of A Clonal Plant Species,Alternanthera Philoxeroides,during The Acclimation With Contrasting Temperatures And Its Adaptive Significance

Many invasive plant species can propagate by clonal growth.Despite the relative low levels of genetic diversity,they often occupy diverse habitats across the world.Epigenetic variation may play an important role during the adaptation to heterogeneous environments.Alternanthera philoxeroides is an invasive alien weed in China.Without genetic variation,it is spreading by clonal growth across the broad areas to the south of Yellow River,including different climatic zones.The acclimation via epigenetic variations to different temperatures might be critical during the invasion of A.philoxeroides.However,only few case studies so far have been conducted to examine the epigenetic modifications in response to environmental changes.In this study,we sampled 8 populations of A.philoxeroides along the coldest monthly minimum temperature gradient in China,including two populations in temperate regions(Jinan and Luoyang),three in subtropical regions(Shanghai,Nanchang and Kunming)and three in tropical regions(Jinghong,Beihai and Sanya),i.e.JN and LY,etc.The epigenetic variation of these wild populations were analyzed using MSAP markers.In the acclimation experiment,all samples were cultivated in two growth chambers with simulated the yearly climate conditions of Jinan(representing warm temperate region)and Haikou(representing tropical regions).,respectively.Asexal generations were calculated as clonal propagation in growth chambers.The first and fourth generation(G1 and G4)during acclimation were analyzed using MSAP markers to examine the dynamic changes of DNA methylation variation.Finally,a reciprocal transplant experiment was conducted using the acclimatized populations to investigate the perfor:mance of key functional traits and its potential contribution to temperature adaptability.The main results of this study are as follows:(1)The epigenetic differentiation of DNA methylation among wild populations of A.philoxeroides may be related to temperature adaptation.PCoA analysis on the MSAP data showed that the samples from different wild populations divided into three groups,which coincided with geographical distribution of populations.(2)The differentiation of DNA methylation among wild populations of A philoxeroides showed transient stability in growth chamber with simulated contrasting climates.However,this pattern became less obvious during the acclimation experiment,especially in the growth chamber with low temperature stress(i.e.Jinan climate).These results suggested that the epigenetic variation observed in wild populations cannot be explained by accumulated random epimutations.In stead,it may result from the active responses or adaptations of the plant to different temperatures.(3)Obvious differences were found in the stem length,number of lateral buds and leaves shape of A.philoxeroides in two growth chambers with contrasting climates,which may be of adaptive significance.Reciprocal transplant experiment showed that the plants in chamber with simulated Jinan's climate had fewer lateral buds,fewer leaves,and longer stem length.These results suggested that the acclimations under different temperatures may produce different phenotypic variation patterns which may be of adaptive importance.Taken together,our study revealed an interesting patter of epigenetic variation of A.philoxeroides across different climate areas,providing preliminary evidence for active adjustment of epigenetic variation to different temperate acclimation.These epigenetic change,together with phenotypic variation,may help this clonal plant to acclimation in different climate areas.These results deepen our understanding of the role of epigenetic variation in the adaption of clonal plants,which are helpful for better management of invasive A.philoxeroides.