DNA Methylation Variations And The Subsequent Adaptational Significance Of Clonal Plant Hierochloe Glabra Trin. Under Heterogeneous Environment

As a prominent epigenetic modification, cytosine methylation may play criticalroles in the adaptational process of plants in response to different environments.Controllable potted plants and MSAP were used to detect the effects of differentgradient of nitrogen addition on the DNA cytosine methylation in Hierochloe glabraTrin. This study was sought to investigate possible impacts of differential levels ofnitrogen supply on cytosine methylation levels of a clonal plant, H. glabra. The mainaim was to interpret the correlations between DNA cytosine methylation and thefitness mechanisms of clonal plant under heterogeneous habitats from the epigeneticview.The experiment was conducted in an open-ended greenhouse, and two types ofenvironments (homogeneous and heterogeneous conditions) were created. Wesimulated the natural heterogeneity of resources by adding different levels of nitrogen.The pots (60cm in diameter and20cm in depth) were divided into four equalcompartments (patches) by plastic partitions and nitrate concentrations at0,0.15,0.30and0.45g N kg-1soil, respectively, were applied. The four compartments weremarked as no nitrogen (NN), low nitrogen (LN), medium nitrogen (MN) and highnitrogen (HN) patches. Homogeneous pots without nitrogen addition were used forcontrol (CK). These clones with same genetic bases were transplanted randomly intothe center areas of the pots, giving each compartment a priori equal chance of beingcolonized.Measurement of morphologic indexes showed the SLA in MN patch wassignificantly higher than others (p=0.008), nitrogen addition did not change budnumber, total biomass, rhizome length, ramet height ramet number and spacer lengthmarkedly. Ramets growing in CK patch showed significantly higher total methylationlevels (p=0.027). Thereinto, CG/CHG methylation levels in NN, LN, MN and HNpatches were27.93%/11.51%,27.92%/11.49%,27.94%/11.38%and27.63%/11.39%,respectively, and in CK patch were27.92%/11.83%. Multiple comparison analysis byDuncan showed that CHG methylation level in CK patch was significantly higherthan the four treatment patches (p=0.026). However, these differences were notsignificant at CG methylation level (p=0.556). The total methylation variation ratiosof ramets in NN, LN, MN and HN patches compared with the control patch were2.51%,2.69%,2.65%and2.91%, respectively, which had no substantially differences (p=0.474), while there was an obviously ascending tendency in accordance with theirnitrogen levels. UPGMA cluster analysis of MSP showed that most of the individualsfrom the same patch clustered together, while three samples of NN patch were farfrom each other. All the15samples were divided into CK and treatment groupsexcept for the CK-3. Cluster analyses further showed that the different amount ofnitrogen addition not only induced epigenetic divergence between treatment andcontrol plants, but also among individuals within treatments. Significant linearregression relationships between cytosine methylation levels and bud number,rhizome length and biomass were found. The sequence analysis of differentiallymethylated DNA bands showed that five bands were homologous to known-functiongenes encoding NADH dehydrogenase, sterol demethylase, hypothetical protein andone was homologous to unknown-function gene.Nitrogen addition reduced the DNA cytosine methylation levels of clonal plants.In natural ecosystems, the change of cytosine methylation levels might play a role inthe process of adaptation to heterogeneous environments. Clonal plants might startupepigenetic variations to adjust morphological variations to guarantee the survival ofthe ramets placed in adverse habitats under external heterogeneous distribution ofnutrients. In addition, epigenetic variations might activate the potential asexualreproduction to produce more offspring ramets, and to expand plant population, whichmight help the clonal plant to live in intense heterogeneous soils and may explain theappearance of H. glabra as a main species in the meadow steppe of Songnen Plain,where severe patchy resource distribution occurs.