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

[02:15 . 78]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。成为寄生虫的植物会抑制或失去它们的光合作用器官，转而依赖寄主物种提供碳、氮和水。除了一个例外，寄生现象是开花植物所特有的，至少在11个谱系中发现了寄生物种。植物科是根寄生的一个分支，包括完全寄生（全寄生）的扫帚花和部分寄生（半寄生）的无花果。在半寄生虫科中，单一的自养谱系显然产生了半寄生虫，而全寄生物种起源于不同的半寄生虫谱系。因此，可以研究一系列从自养到半寄生和从半寄生到全寄生的转变，以了解这种生活方式转变背后的步骤。初步证据表明，这些寄生虫光合机制的发育可能受到光合作用上游遗传调控因子的抑制。这将使光合能力受到抑制，但不会丧失。为了验证这一模型，需要一个改进的系统发育关系假说。将收集和分析该家族大多数属的核和叶绿体基因的DNA序列数据，以确定其系统发育历史。核DNA测序的重点将放在光敏色素基因上，这些基因编码光感受器，参与调节光合基因的表达和发育。因此，为解决系统发育问题而收集的数据也可用于测试光敏色素光感受器功能改变在寄生虫发育中的作用。具体来说，将评估光敏色素基因拷贝数、分子进化和在半和全寄生虫以及自养亲属中的表达，以确定光敏色素功能是否改变。在没有全部或部分光合作用机制的情况下生存的能力产生了寄生杂草，严重影响了全世界的农业和林业，但植物成为寄生虫的步骤仍然未知。因此，控制它们的机制仍然不发达。一个被广泛接受的模型表明，基因丢失导致了全寄生。但是这并不能完全解释为什么一些全寄生植物保留了完整的光合基因，也不能解释为什么大多数寄生开花植物保留了光合能力。一个涉及光合作用抑制但不丧失的模型可能更好地解释这些数据。这些基于光敏色素基因序列、核糖体和质体位点序列的研究，将提高我们对花椰菜科植物系统发育的认识，并为检验植物寄生进化模型提供一个健全的系统发育框架。

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.