Origin and co-evolution of land plant-fungal symbioses through the "greening of the Earth"

陆地植物对陆地的定居。475 Ma是地球历史上影响最深远的篇章之一。苔类植物在陆地植物进化树中占据着举足轻重的地位，有各种各样的证据支持这些非维管植物作为最基本的陆地光合生物，并在最早的殖民者的土地约。475马。最近的分子遗传学证据支持这样的观点，即地钱中的菌根样协会是一个基础和祖先的性状，陆地植物从一个单一的共同祖先进化而来，在根进化之前与真菌伙伴形成共生协会。至少在过去的30年里，普遍的范式一直是AM真菌是与最早的陆地植物共同进化的所有植物-真菌共生体的祖先形式。AM菌群是最常见的菌根类型，目前在70%以上的陆地植物物种中发现，包括简单和复杂的叶状苔类。然而，项目小组成员（MB，JGD，SP）报告的新证据表明，最基础的现存苔类，单胞菌纲，只与最基础的植物共生真菌-内生菌目形成联系。我们现在第一次有证据表明，真菌群在与陆地植物营养共生的黎明时就已经存在。这打开了一个显着的新窗口，功能调查如何共生促进了陆地biosepher. We的建议，利用这些发现，解决三个基本的进化问题有关的初始阶段的植物“绿化地球”：（1）之间的协会地钱和物种的Endogone功能等同于那些形成AM真菌的合作伙伴？(2)真菌的合作伙伴从faculitarisaprotrophic Endogone专性生物营养AM真菌通过进化的基础苔类植物和真菌的互利互惠的利益驱动的进展？(3)土壤有机质的积累是否有利于专性生物营养型AM真菌向植物提供矿质营养？我们精心挑选了7种苔类真菌协会，提供了一个强大的频谱模型系统，适合实验和定量功能分析的C交换，营养关系和真菌特异性。我们所有的目标生物都可以从孢子或芽中培养出来，为植物提供或不提供真菌共生体。这提供了一个强大的方法，使量化的配子体生长，营养和生殖输出在3年的项目内的真菌定植。我们的实验计划将在（1）成熟的田间收集的种群和（2）共生与非共生植物从芽/孢子生长。现场收集的人口将用于功能研究的C-分配从苔类植物到他们的真菌合作伙伴和相互吸收的营养物质进入植物通过真菌。来自芽/孢子的种群将用于调查真菌共生体对苔类植物的生长和繁殖产出以及真菌伴侣的生物量和程度的净成本/效益。分子鉴定和超微结构的研究将进行两套植物，以建立真菌内共生体的身份，植物-真菌界面的性质，以及这些如何与功能和宿主特异性。总的来说，该项目将为陆地植物和真菌之间古老共生的曙光提供基础知识和理解，这种共生在陆地生态系统的进化中发挥了奠基作用-这一主题与NERC的地球系统科学主题高级别挑战“提高当前对生命进化与地球之间相互作用的认识”密切相关。

Colonization of the land by terrestrial plants ca. 475 Ma was one of the most far-reaching chapters in Earth's history. Liverworts occupy the pivotal position in the land plant evolutionary tree with a wide variety of evidence supporting these non-vascular plants as the most basal terrestrial photosynthetic organisms and amongst the earliest colonizers of the land ca.475 Ma. Recent molecular genetic evidence supports the view that mycorrhiza-like associations in liverworts are a basal and ancestral trait, and land plants evolved from a single common ancestor that formed symbiotic associations with fungal partners before roots evolved. For at least the past 30 years, the prevailing paradigm has been that AM fungi are the ancestral form of all plant-fungal symbioses co-evolving with the earliest land plants. AM associations are the most common type of mycorrhiza, and are currently found in over 70% of land plant species including simple and complex thalloid liverworts. However, new evidence reported by members of the project team (MB, JGD, SP) has revealed that the most basal extant groups of liverworts, the Haplomitriopsida, exclusively form associations with the most basal group of plant-symbiotic fungi - the Endogonales. For the first time, we now have evidence pointing to the identity of the fungal group at the dawn of their nutritional symbiosis with land plants. This opens a remarkable new window for functional investigations into how the symbiosis facilitated the emergence of the terrestrial biosphere.Our proposal exploits these findings by addressing three fundamental evolutionary questions relating to the initial phase of plants 'greening of the Earth': (1) Are the associations between liverworts and species of Endogone functionally equivalent to those formed with AM fungal partners? (2) Was the switching of fungal partners from facultatively saprotrophic Endogone to obligately biotrophic AM fungi through the evolutionary advance of basal liverworts driven by increasing mutualistic benefits to the plants and fungi? (3) Did the accumulation of soil organic matter favour obligately biotrophic AM fungi over facultatively saprotrophic Endogone in supplying mineral nutrients to the plants?We have carefully selected 7 liverwort species with fungal associations that provide a powerful spectrum of model systems amenable to experimentation and quantitative functional analyses of C exchange, nutrient relationships and fungal specificity. All of our target organisms can all be cultured either from spores or gemmae to provide plants with and without fungal symbionts. This provides a robust approach for enabling quantification of fungal colonization on gametophyte growth, nutrition and reproductive output within a 3 yr project. Our experimental programme will be conducted on (1) mature field-collected populations and (2) symbiotic vs. asymbiotic plants grown from gemmae/spores. Field collected populations will be used for functional studies of C-allocation from liverworts to their fungal partners and reciprocal uptake of nutrients into the plants via the fungi. Populations from gemmae/spores will be used for investigating the net costs/benefits of the fungal symbionts on the growth and reproductive output of the liverworts and the biomass and extent of the fungal partners. Molecular identification and ultra-structural studies will be undertaken on both sets of plants to establish the identity of the fungal endosymbionts, the nature of the plant-fungal interfaces, and how these relate to function and host specificity. Overall, this project will contribute fundamental knowledge and understanding to the dawn of an ancient symbiosis between land plants and fungi that played a founding role in the evolution of terrestrial ecosystems - a topic closely aligned to NERC's Earth System Science Theme high-level challenge "improving current knowledge of the interaction between the evolution of life and the Earth".