Dissertation Research: Anthocyanin Biosynthesis and the Evolution of Red-Flowered Ipomoea

高大牵牛花(Ipomoea Purpurea)天然居群常被一种真菌病原菌--炭疽菌侵染。这种植物只有一个基因和两个等位基因，它们要么完全抵抗感染，要么对感染敏感。这两个等位基因在高大牵牛花的自然种群中都有表现，这一模式在许多野生植物物种中都能找到。这一观察结果与直觉预测相矛盾，即提供对有害病原体的抗性的等位基因的频率应该接近1。为解释抗性/感病等位基因悖论而提出的假说表明，当病原菌种群是动态的时，抗性等位基因的净收益是由内在成本调节的。这个项目将使用田间实验来探索高大牵牛花中抗性等位基因的潜在条件益处。这项工作试图用抗性/易感等位基因悖论作为案例研究来解释自然选择如何维持遗传变异。除了有助于解决进化生物学中的一个基本问题外，这项工作也可能适用于历史上从作物野生祖先那里整合抗性等位基因的作物育种者。随着许多国家对转基因作物越来越持怀疑态度，人们再次需要了解自然选择如何作用于自然种群中的抗性等位基因，以便更好地利用现有的抗病作物，并更好地保护抗性等位基因所代表的自然资源。

Rausher0107172Natural populations of the tall morning glory (Ipomoea purpurea) are commonly infected by a fungal pathogen, Coleosporium ipomoeae. This plant has a single gene with two alleles that condition either complete resistance or susceptibility to infection. Both alleles are represented in natural populations of the tall morning glory, a pattern found in many wild plant species. This observation contradicts the intuitive prediction that an allele providing resistance against a harmful pathogen should approach a frequency of one. Hypotheses proposed to explain the resistance/susceptibility allele paradox suggest the net benefit of a resistance allele is mediated by inherent costs when the pathogen population is dynamic. This project will use field experiments to explore the potentially conditional benefits of the resistance allele in the tall morning glory. This work attempts to explain how natural selection may act to maintain genetic variation using the resistance/susceptibility allele paradox as a case study. In addition to contributing to the resolution of a fundamental issue in evolutionary biology, this work may also have applications to crop breeders who have historically incorporated resistance alleles from the wild progenitors of crop plants. As many countries become increasingly skeptical of transgenic crops, there is a renewed need to understand how natural selection acts on resistance alleles in natural populations, both to better utilize current resistant crops and to better conserve the natural resource that resistance alleles represent.