DISSERTATION RESEARCH: Genetic Effects of Plant Defense on Above- and Below-ground Ecological Interactions and Natural Selection

研究人员将使用一种原产于落基山脉的芥菜科植物——严格的芥菜科植物（Boechera stricta），测试不同环境下自然选择机制的差异如何影响天然植物化学防御变异的维持。在自然种群中，个体间性状变异的持久性使得适应得以发生。尽管变异在适应过程中起着核心作用，但面对自然选择淘汰不太适合的品种，变异如何以及为什么会持续存在，人们知之甚少。化学防御策略（不同类型和浓度的芥菜油）在研究物种的自然种群中是高度可变的。这些防御性化合物具有已知的生态效应，既可以作为昆虫取食树叶的威慑物（地上效应），也可以作为土壤微生物群落组成的驱动因素（地下效应）。研究人员将测试植物生长和繁殖是如何受到不同化学防御策略对植物-昆虫和植物-微生物相互作用的地上和地下影响的。该项目为本科生培训提供了机会。计划中的外展活动将针对初高中学生，以及在冠顶丘野花节期间的公众。植物防御化学物质的多效性及其背后的基因已被充分证明。除了通过在地上环境中调节草食来影响适应性外，防御性化学物质还可以影响根组织周围土壤中的微生物群落。地上和地下选择压力之间的相互作用可能影响植物化学自然选择的总体模式。研究人员将利用生态模式物种（芸苔科）的近等基因系来测试化学防御基因在地上和地下的多效性效应，这些物种在控制芥菜油生物合成的基因上有所不同。他们将首先描述防御化学剖面对根际微生物群落聚集的影响。其次，他们将评估根际选择如何影响植物适应性。最后，他们将测试地下环境如何改变芥菜油作为抗食草动物防御的地上效应，以及芥菜油的地上和地下适应性效应之间的相互作用如何导致遗传和性状多样性在空间和时间上的维持。

Using a plant species native to the Rocky Mountains in the mustard family, Boechera stricta, the investigators will test how differences in mechanisms of natural selection across environments influences the maintenance of variation of natural plant chemical defenses. In natural populations, the persistence of variation of traits among individuals allows for adaptation to occur. Despite the central role of variation in the process of adaptation, it is poorly understood how and why variation persists in the face of natural selection eliminating less fit varieties. Chemical defense strategies (various types and concentrations of mustard oils) are highly variable across natural populations of the study species. These defensive compounds have known ecological effects, both as deterrents of insect feeding on leaves (above-ground effects) and as drivers of microbial community composition in the soil (below-ground effects). The researchers will test how plant growth and reproduction are influenced by the above- and below-ground effects of different chemical defense strategies on plant-insect and plant-microbe interactions. The project provides opportunity for undergraduate training. Planned outreach activities will target middle and high school students, and also the general public during the Crested Butte Wildflower Festival.The pleiotropic effects of plant defensive chemicals and the genes that underlie them are well documented. In addition to influencing fitness by mediating herbivory in aboveground environments, defensive chemicals can affect microbial communities in the soil immediately surrounding root tissue. It is likely that interactions between above- and belowground selective pressures influence overall patterns of natural selection on plant chemistry. The investigators will test for pleiotropic above- and belowground effects of a chemical defense gene utilizing near-isogenic lines of the ecological model species, Boechera stricta (Brassicaceae), that vary in a gene controlling mustard oil biosynthesis to. They will first characterize the effects of defensive chemical profiles on microbial community assembly in the rhizosphere. Second, they will assess how rhizosphere selection affects plant fitness. Finally, they will test how the belowground context may modify aboveground effects of mustard oils as anti-herbivore defenses, and how interactions between the above- and belowground fitness effects of mustard oils result in the maintenance of genetic and trait diversity over space and time.