Phylogeny of Orobanchaceae Sensu lato Inferred from Phytochromes and Other Data: Implications for the Evolution of Parasitism

从光敏色素和其他数据推断列当科的系统发育：对寄生进化的影响

• 批准号: 0215780
• 负责人: Sarah Mathews
• 金额: $ 26万
• 依托单位: University of Missouri-Columbia
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-09-01 至 2004-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0215780&HistoricalAwards=false
• 关键词: Phylogeny; Orobanchaceae; Sensu; lato; Inferred

0215780Mathews and Wolfe By definition, plants are autotrophic organisms, capable of producing their own food via photosynthesis. Plants that become parasites suppress or lose their photosynthetic apparatus and come to rely on host species for carbon, nitrogen, and water. With a single exception, parasitism is unique to flowering plants, where parasitic species are found in at least eleven lineages. The plant family Orobanchaceae is a lineage of root parasites that includes the completely parasitic (holoparasitic) broomrapes and the partially parasitic (hemiparasitic) figworts. Within Orobanchaceae, a single autotrophic lineage apparently gave rise to the hemiparasites, and holoparasitic species have originated from different hemiparasitic lineages. Thus, a series of transitions from autotrophism to hemiparasitism and from hemi- to holoparasitism can be investigated to learn about the steps underlying this switch in lifestyle. Preliminary evidence suggests that development of the photosynthetic machinery in these parasites may be suppressed by upstream genetic regulators of photosynthesis. This would allow photosynthetic capacity to be suppressed but not lost. To test this model, an improved hypothesis of phylogenetic relationships within Orobanchaceae is required. DNA sequence data from nuclear and chloroplast genes sampled from the majority of genera in the family will be collected and analyzed to resolve their phylogenetic history. The focus of the nuclear DNA sequencing will be on phytochrome genes, which encode photoreceptors involved in regulating photosynthetic gene expression and development . Thus, data collected to address phylogenetic questions can also be used to test the role of altered phytochrome photoreceptor function in the development of parasites. Specifically, phytochrome gene copy number, molecular evolution, and expression in hemi- and holoparasites and in autotrophic relatives will be assessed to determine whether phytochrome function is altered. The capacity to exist without all or part of the photosynthetic machinery has given rise to parasitic weeds that significantly impact agriculture and forestry throughout the world, but the steps whereby plants become parasites remain unknown. Thus, mechanisms for their control remain underdeveloped. A widely accepted model suggests that gene loss leads to holoparasitism. But this does not fully explain the retention of intact photosynthetic genes by some holoparasites, nor does it explain why most parasitic flowering plants retain photosynthetic capacity. A model involving suppression but not loss of photosynthesis may better explain the data. These studies based on sequences from phytochrome genes, supplemented with sequences from nuclear ribosomal and plastid loci, will improve our understanding of phylogeny in Orobanchaceae and will provide a sound phylogenetic framework for testing models for the evolution of parasitism in plants.

0215780马修斯和沃尔夫根据定义，植物是自养生物，能够通过光合作用生产自己的食物。 成为寄生虫的植物抑制或失去光合作用机构，并依赖宿主物种获得碳，氮和水。 除了一个例外，寄生是显花植物所独有的，其中寄生物种至少存在于11个谱系中。 列当科植物是根寄生植物的一个谱系，包括完全寄生（全寄生）的肉苁蓉和部分寄生（半寄生）的玄参。 在列当科，一个单一的自养谱系显然引起了半寄生，和全寄生物种起源于不同的半寄生谱系。 因此，一系列的过渡，从自养半寄生和从半到全寄生，可以调查了解的步骤，这种转变的生活方式。 初步证据表明，这些寄生虫的光合作用机制的发展可能受到上游光合作用遗传调节因子的抑制。 这将使光合能力受到抑制，但不会丧失。 为了检验这个模型，需要一个改进的假设列当科内的系统发育关系。 将收集和分析从该科大多数属中取样的核和叶绿体基因的DNA序列数据，以解决它们的系统发育历史。 核DNA测序的重点将放在光敏色素基因上，光敏色素基因编码参与调节光合基因表达和发育的光感受器。 因此，收集的数据，以解决系统发育问题，也可以用来测试的作用，改变光敏色素感光功能的发展中的寄生虫。 具体而言，光敏色素基因的拷贝数，分子进化，并在半和全寄生虫和自养亲属的表达将进行评估，以确定光敏色素功能是否被改变。在没有全部或部分光合作用机制的情况下生存的能力已经引起了寄生杂草，这些寄生杂草对世界各地的农业和林业产生了重大影响，但植物成为寄生虫的步骤仍然未知。 因此，控制这些人的机制仍然不发达。 一个被广泛接受的模型表明，基因丢失导致全寄生。 但这并不能完全解释某些全寄生植物保留完整的光合作用基因，也不能解释为什么大多数寄生开花植物保留光合作用能力。 一个涉及光合作用抑制但不损失的模型可能更好地解释这些数据。 这些研究的基础上，从光敏色素基因的序列，补充从核核糖体和质体基因座的序列，将提高我们的理解列当科的寄生性，并将提供一个健全的系统发育框架测试模型在植物中的寄生进化。