东亚特有植物领春木的景观基因组学研究

Adaptation is one of the most important strategies for tree species in the face of climate change. However, the genetic basis of adaptation has often been neglected, especially in non-model tree species for which genomic information is limited or absent. In parallel with technical progress made in sequencing methods, landscape genomics has offered an empirical approach to detect climate factors driving the process of adaptation. In this project, we will genotype single nucleotide polymorphisms (SNPs) in 15 to 20 populations of Euptelea pleiospermum across its natural range in China and adjacent area. We will apply Paired-End RAD-tag sequencing to identify SNP markers. Based on the average latitude and longitude for each sampling site, climate data will be obtained from the Ecological Database of Chinese Ecosystem Research Network (CERN). First, we will reveal geographic pattern of adaptive diversity and landscape genetic structure of E. pleiospermum at a broad scale. Second, landscape genomics analyses will be used to investigate how climate factors influence patterns of adaptive genetic variation. We will use the association between climate factors and allele frequencies to identify potential loci underlying selection. In other words, after accounting for genetic variation due to demography, or other neutral processes, landscape genomics analyses will be performed to identify loci that are related to climate variables. In general, this project aims to assess the potential of genetic responses to climate change for endemic and rare tree species in subtropical mountains of China. This project will provide critical information for understanding the extent to which climate has shaped geographic genetic structure in the past, and for identifying tree population that may be at risk with the predicted rapid future climate change.

遗传适应性是木本植物应对气候变化的重要策略之一。但是，木本植物响应气候变化的遗传适应潜力往往被忽略，尤其是缺乏基因组信息的非模式植物。随着高通量测序技术的快速发展，植物在气候变化条件下的遗传适应潜力研究逐渐由景观遗传学领域的难点变为热点。本项目拟以领春木（Euptelea pleiospermum）为研究对象，采用单核苷酸多态性（SNP）分子标记技术和景观基因组学分析方法，（1）在分布区尺度上揭示领春木适应性遗传多样性地理格局和景观遗传结构；（2）通过将适应性遗传多样性和遗传结构与气候因子进行关联分析，确定受气候因子影响的基因位点及与之关联的关键气候因子，探讨气候因子在领春木适应性遗传变异形成中的作用。该项目旨在评估气候变化条件下我国亚热带山地珍稀特有木本植物的遗传适应潜力。该项目的开展不仅可以促进景观遗传学理论的发展和完善，也为气候变化条件下我国亚热带山地珍稀植物的保护提供新的理论依据。

本项目以东亚特有植物领春木（Euptelea pleiospermum）为研究对象，整合简化基因组测序手段、叶片功能性状数据和环境变量，对该物种在分布区尺度上对气候和土壤的遗传适应潜力进行研究。主要开展以下几方面的研究：（1）领春木对土壤和气候因子的局域适应性：基于景观基因组学的证据；（2）领春木种群应对环境变化的适应策略：进化差异与表型可塑性；（3）不同纬度山地领春木遗传变异的海拔梯度格局。研究结果如下：（1）基于简化基因组测序数据，领春木的种群遗传结构与前期SSR数据的分析基本一致。基于景观基因组学方法分析，领春木在分布区尺度上对气候因子，而非土壤pH值、碳氮磷钾含量等土壤因子，具有一定程度的适应性。就气候因子而言，领春木对年均温、年降水量、昼夜节律、温度和降水的季节性没有明显的适应性，但是对最冷月最低温、最冷季度均温、最干季度降水量和最冷季度降水量等季度温度很可能存在一定程度的适应性。（2）在中国分布区内，与领春木叶片大小的相关性状发生了进化上的差异，北方种群进化出较大的叶片，温度变量和土壤总磷含量是驱动性状差异的主要因子。而资源获取策略和营养分配策略相关的性状差异并未发生遗传学的差异，推测这类性状变化是可塑性的变化。（3）领春木种群的遗传多样性沿高（秦岭33°N）、低（峨眉山29°N）纬度山地并未呈现明显的海拔梯度格局，沿中纬度（神农架31°N）山地则呈现“中间高、两端低”的海拔梯度格局。沿高、低纬度山地并未呈现明显的遗传结构，沿中纬度山地则被明显划分为高海拔和低海拔两个遗传群体。沿中纬度山地的当代基因流显著低于高、低纬度山地。距离隔离检验沿3座山均不显著，同时，海拔（环境）隔离检验仅在中纬度山地显著。以上结果表明，冰期历史事件在领春木海拔梯度格局形成中作用较弱；不同纬度山地的空间隔离程度、生态稳定性和植被类型差异在很大程度上决定了我国亚热带山地珍稀植物的海拔梯度格局。