Clone History Shapes Populus Drought Responses

Just as animal monozygotic twins can experience different environmental conditions by being reared apart, individual genetically-identical trees of the genus Populus can also be exposed to contrasting environmental conditions by being grown in different locations. As such, clonally-propagated Populus trees provide an opportunity to interrogate the impact of individual environmental history on current response to environmental stimuli. To test the hypothesis that current responses to an environmental stimulus, drought, are contingent on environmental history, the transcriptome-level drought responses of three economically important hybrid genotypes: DN34 (Populus deltoides x P. nigra); Walker (P. deltoides var. occidentalis x (P. laurifolia x P. nigra)); and, Okanese (‘Walker’ x (P. laurifolia x P. nigra)) derived from two different locations were compared. Strikingly, differences in transcript abundance patterns in response to drought were based on differences in geographic origin of clones for two of the three genotypes. This observation was most pronounced for the genotypes with the longest time since establishment and last common propagation. Differences in genome-wide DNA methylation paralleled the transcriptome level trends, where the clones with the most divergent transcriptomes and clone history had the most marked differences in the extent of total DNA methylation, suggesting an epigenetic basis for the clone-history-dependent transcriptome divergence. The data provide insights into the interplay between genotype and environment in the ecologically and economically important Populus genus, with implications for both the industrial application of Populus trees, and the evolution and persistence of these important tree species. 72 arrays total. 2 time points. 2 water regimes. 3 biological replicates per treatment

正如动物的同卵双胞胎因分开饲养而遭遇不同环境条件一样，杨属（*Populus*）的遗传同源个体树木也可因种植于不同地点而暴露于迥异的环境之中。故此，通过无性繁殖得到的杨树可为探究个体环境历史对当前环境刺激响应的影响提供契机。为验证「当前对环境刺激（干旱）的响应取决于个体环境历史」这一假说，本研究对3个具有重要经济价值的杂交基因型杨树——DN34（美洲杨×欧洲黑杨，*Populus deltoides* × *P. nigra*）、Walker（西方美洲杨×（劳氏杨×欧洲黑杨），*P. deltoides* var. *occidentalis* × (*P. laurifolia* × *P. nigra*)）以及Okanese（‘Walker’ ×（劳氏杨×欧洲黑杨））——来自两个不同种植地点的干旱响应转录组（transcriptome）水平数据进行了比较。值得注意的是，三个基因型中有两个的干旱响应转录本丰度模式差异，取决于其无性系的地理起源差异。该现象在定植时间与末次共同繁殖间隔最长的基因型中表现最为显著。全基因组DNA甲基化（DNA methylation）差异与转录组水平的变化趋势一致：转录组差异与无性系历史差异最大的无性系，其总DNA甲基化程度差异也最为显著，这表明依赖无性系历史的转录组分化存在表观遗传（epigenetic）基础。本数据集为探究兼具生态与经济价值的杨属中基因型与环境之间的互作关系提供了新视角，其研究结果对杨树的工业化应用以及该重要树种的演化与存续均具有参考意义。实验共包含72张基因芯片，设置2个时间点、2种水分处理，每组处理设置3个生物学重复。