入侵植物黄顶菊DNA表观遗传多样性及其生态适应性的机理研究

Flaveria bidentis is one of the major alien plants that have been introduced to North China in recently years and its strong ability to adapt to the environment is closely related to its invasiveness. Phenotypic plasticity has long been suspected to allow invasive species to expand their geographic range across large-scale environmental gradients. Epigenetic variation is one of the main molecular mechanisms that can contribute to environmental adaptability and phenotypic plasticity. However, few studies have focused on epigenetic diversity of Flaveria bidentis genome DNA at the present time. Therefore, DNA methylation was taken as an epigenetic marker and by methylation-sensitive amplified polymorphism (MSAP) technique, temporal and spatial variation characteristics of epigenetic diversity for different organs and different developmental stages were studied. The effects of different geographical distribution and habitat conditions were also investigated. Pot experiments were conducted to simulate the main heterogeneous environmental conditions including light, nitrogen, water and saline-alkaline for Flaveria bidentis growing, so that the phenotypic plasticity responses of morphology features, biomass allocation and physiological indicators can be studied. It was also used to clarify the correlation between the apparent variation of phenotypic plasticity and epigenetic diversity, to reveal the molecular basis of phenotypic plasticity generation, to further speculate the genes or genotypes which may associate with environmental adaptability, and finally to explore the possible epigenetic mechanisms of the ecological adaptability acquirement for the Flaveria bidentis. This project work will provide an important theoretical foundation and a new idea for predicting the potential distribution of Flaveria bidentis, developing prevention strategies and making in-depth research of its invasiveness.

黄顶菊是近年来入侵我国华北地区的主要外来植物，其强的环境适应能力与其入侵性密切相关。表型可塑性影响植物适应不同生境的能力，DNA表观遗传变异是环境适应性获得和表型可塑性实现的重要分子机制之一，然而目前针对黄顶菊DNA表观遗传多样性的研究还鲜有报道。因此，本项目以DNA甲基化为表观遗传标记，采用甲基化敏感扩增多态性（MSAP）技术，研究黄顶菊不同器官和不同发育阶段DNA表观遗传多样性时空变化特征，以及不同地理区域和入侵生境条件对其影响。通过网室控制试验设置光照、氮素、水分和盐碱等模拟黄顶菊生长的主要异质环境条件，研究其形态特征、生物量分配和生理指标的表型可塑性响应，阐明表型可塑性变异与表观遗传多样性之间的相关关系，揭示表型可塑性产生的分子基础，进一步推测与环境适应性相关的基因或基因型，探索黄顶菊生态适应性获得的表观遗传机制，为预测其潜在分布范围、制定防控策略以及深入研究其入侵性提供理论依据。

本项目以DNA甲基化为表观遗传标记，采用甲基化敏感扩增多态性（MSAP）技术，研究黄顶菊种子萌发、组织器官发育过程和不同地理分布区域黄顶菊DNA表观遗传多样性变化特征。同时模拟不同农田施氮梯度、不同盐碱胁迫生境、不同浓度梯度镉、砷单一以及复合污染，研究各种复杂异质生境下黄顶菊生长及生理生态特性的表观遗传变异和表型可塑性响应规律，探讨其耐受性与入侵性之间的关系。结果表明：（1）黄顶菊种子萌发过程中胞嘧啶发生甲基化主要以双链甲基化形式为主，多态性百分比为95.37%，多态性位点数所占总位点数比率为48.95%，DNA甲基化与去甲基化两者共同调控黄顶菊生命初期的生长发育，且去甲基化的变化在种子萌发过程中占主导。（2）不同器官和不同发育阶段的甲基化模式均存在显著差异，黄顶菊根、茎器官间存在一定个体差异，且这种个体间差异大于叶片个体间差异。（3）四个地区黄顶菊种群的遗传分化系数（Gst）为0.07，7%的遗传变异存在于种群间，93%的遗传变异则存在于种群内，基因流（Nm）为3.321（＞1），表明四个不同入侵地区黄顶菊种群间存在广泛而频繁的基因交流。（4）黄顶菊主要通过增加根生物量来吸收土壤中的养分，通过调节自身的营养生长和生殖生长等指标来适应施氮处理；在受到重金属胁迫时，黄顶菊主要通过调节其根生物量、叶生物量、净光合速率、气孔导度、蒸腾速率、过氧化氢酶和电解质外渗率等指标来获得适应性；不同胁迫条件下，以上各指标的表型可塑性指数与DNA甲基化水平表现出极显著相关性。研究入侵植物黄顶菊甲基化变异的分布特征和变化规律、环境差异对DNA表观遗传多样性变化的影响及植物对异质环境的表型可塑性响应规律，有助于明确黄顶菊能够在短时间内快速适应、生长、蔓延和扩散等生态适应性获得的机理，将为预测其潜在的分布范围和制定防控策略，为深入研究其入侵性提供新思路和理论依据。