Dissertation Research: Chloroplast Evolution of the Nonphotosynthetic Liverwort Cryptothallus Mirabilis (Aneuraceae)

摘要在苔藓植物(苔藓、地钱和角菜)中，真菌群落只在角藻和地钱中常见；然而，只有在地钱植物中才有一种完全依赖真菌群落而不是光合作用来获得固定碳的物种。这种对替代碳源的依赖只存在于一种(两种)苔类植物中：隐藻(天南星科)。奇异隐藻不进行光合作用，缺乏绿色素，因此外观呈淡黄色。碳从真菌中被吸收，真菌穿透地钱的细胞间隙。这种名为Tulasnella的真菌通过与松树或桦树的外生菌根结合来满足其碳需求。在开花植物中，非光合作用生命策略的进化伴随着叶绿体基因组的减少。这种减少会导致参与光合作用反应的酶的编码基因丢失(身体上或功能丧失)。该奖项将支持伯纳德·戈菲内博士的研究生诺曼·威克特的论文研究，他调查在非光合作用被子植物中观察到的基因丢失模式是否也存在于非开花陆地植物，特别是苔藓植物中。为了做到这一点，将对奇异华南藻的完整叶绿体基因组以及与其密切相关的光合作用亲缘关系的基因组进行测序。系统发育重建将被用来识别最接近的光合作用地钱，并检验基因组进化的假说。然后，可以在两个叶绿体基因组之间进行比较，以确定与光合作用丧失相关的变化，并检验基因组进化的假说。利用为非光合花植物开发的改进的鸟枪测序方法获得叶绿体基因组序列。本研究将基因组学和系统发育学结合起来，以评估非光合作用苔藓植物叶绿体基因组进化的模式。目前在这一领域的许多认识都来自于对开花植物的研究；因此，这项研究将极大地拓宽研究伴随着生命最基本过程之一光合作用的丧失而发生的叶绿体基因组进化的分类多样性。这项研究的结果将向公众和科学界公布。在后一种情况下，这些结果将对目前总体上解决陆地植物进化的研究提供特别的信息。这项研究独特的自然历史及其重点问题(失去主要选择力量时的基因组进化)的基本性质，应有助于通过地方外联活动和在大众期刊上发表出版物来传播研究结果。

AbstractWithin bryophytes (mosses, liverworts, and hornworts), fungal associations are common only in hornworts and liverworts; however, only among liverworts is there a species that relies entirely on its fungal associate, rather than on photosynthesis, for fixed carbon. This dependence on an alternative carbon source is present only in one genus (two species) of liverworts: Cryptothallus (Aneuraceae). Cryptothallus mirabilis is non-photosynthetic, lacks the green pigment chlorophyll, and is therefore whitish yellow in appearance. Carbon is taken up from the fungus, which penetrates the intercellular spaces of the liverwort. The fungus, Tulasnella, satisfies its carbon demand through and ectomycorrhizal association with pine or birch trees. Among flowering plants, the evolution of a non-photosynthetic life strategy is accompanied by a reduction in the chloroplast genome. This reduction results in the loss (physically, or loss of function) of genes that code for enzymes involved in the reactions of photosynthesis. This award will support the dissertation research of a graduate student of Dr. Bernard Goffinet, Norman Wickett, investigating whether the patterns of gene loss observed in non-photosynthetic angiosperms are also present in non-flowering land plants, particularly bryophytes. To accomplish this, the complete chloroplast genome of C. mirabilis will be sequenced, as well as that of a closely related photosynthetic relative. Phylogenetic reconstruction will be used to identify the most closely related photosynthetic liverwort and to test hypotheses of genomic evolution. Comparisons can then be made between the two chloroplast genomes in order to identify changes associated with the loss of photosynthesis and to test hypotheses of genomic evolution. Chloroplast genome sequences will be obtained using a modified shotgun sequencing method developed for non-photosynthetic flowering plants.This study integrates genomics and phylogenetics in order to assess patterns of chloroplast genome evolution in a non-photosynthetic bryophyte. Much of the current understanding in this area arises from studies of flowering plants; this study, therefore, will significantly broaden the taxonomic diversity of studies addressing chloroplast genome evolution accompanying the loss of one of the most fundamental processes of life: photosynthesis. The results of this study will be made available to the public and the scientific community. In the latter case, the results will be particularly informative to current studies addressing the evolution of land plants in general. The unique natural history of this study, and the fundamental nature of its focal questions (genomic evolution when major selection forces are lost), should facilitate the dissemination of findings through local outreach activities and publications in popular journals.