SHIFTING SYMBIOTIC SCENARIOS AT THE DAWN OF LAND PLANT-FUNGUS ASSOCIATIONS

植物在地球陆地上的殖民超过475 Ma，极大地改变了陆地生物圈的发展，对随后的所有陆地生命产生了深远的影响。人们普遍认为，共生真菌促进早期植物陆生化，通过增加获得矿物营养素，以换取光合作用固定的有机碳。我们最近的发现带来了问题，迄今假定的身份，生物学和功能的真菌共生体的最早分歧谱系现存的陆地植物。我们的项目解决了这些基本的知识差距，包括从我们以前的研究中产生的关于植物-真菌协会的调节和兼容性的关键新问题。该项目有望对植物、微生物和土壤相互交织的过去、现在和未来进行有趣的发现。今天超过80%的植物与土壤真菌Glomeromycota相关联，形成互利的伙伴关系，称为丛枝菌根（AM）。这些合作伙伴关系涉及将通过光合作用产生的植物糖转移给真菌伙伴，以换取真菌从土壤中的矿物质中开采的必需营养素。大约4.75亿年前，当第一批无根植物从水中出现在陆地上时，人们认为合作真菌提供了植物在陆地上生长所需的营养。该项目团队成员最近的研究表明，地球上一些进化上最古老的植物，苔类，与真菌形成了伙伴关系，这些真菌可能比AM更古老。这些真菌被称为毛霉亚门。我们的研究结果表明，地钱和毛霉亚门真菌之间的关联可能是祖先的菌根共生，铺平了道路的陆地环境的植物和复杂的陆地生态系统的进化，我们今天所熟悉的殖民。同样有可能的是，最早的陆地植物实际上同时与毛霉亚门和AM真菌有关，就像今天的一些植物一样。30多年来，人们一直把AM作为祖先植物-真菌共生体来关注，但随着我们最近令人惊讶地发现另一种全球广泛和古老的关联，我们有独特的机会和迫切的需要来了解一种对地球上的生命具有潜在无数影响的新生物学。通过使用来自不同科学领域的尖端和新颖的方法，我们的研究将对两组真菌与几个主要陆地植物群体之间的合作的功能和兼容性产生重要的见解。我们的实验将在不同的大气CO2浓度下进行，反映地球上CO2浓度在进化过程中的变化，为现代植物-真菌共生体的结构、功能和进化提供令人兴奋的新见解。通过对CO2与不同土壤真菌之间相互作用的更深入的机制和进化理解，我们的研究扩展到土壤生态学、植物-土壤过程、并可能导致更有效的保护战略（见影响途径文件）。通过研究不同陆地植物群体共生的生理反应，这项研究将有助于理解和预测这些系统对大气CO2浓度持续变化的反应; NERC气候系统和生物多样性战略中的重要考虑因素，并对粮食安全和土壤生态产生重大影响。展望未来，我们通过这项研究开发和测试的技术和假设可以转移到植物王国中其他具有经济重要性的共生体中，例如作物的真菌疾病和在作物中使用菌根用于未来的可持续农业。

Plants colonised Earth's landmasses more than 475 Ma, drastically altering the development of the terrestrial biosphere, with far-reaching consequences for all subsequent terrestrial life. It is widely thought that symbiotic fungi facilitated early plant terrestrialisation by enhancing access to mineral nutrients in exchange for photosynthetically-fixed organic carbon. Our recent discoveries have brought into question the hitherto-assumed identity, biology and function of the fungal symbionts of the earliest diverging lineages of extant land plants. Our project addresses these fundamental knowledge gaps, including critical new questions arising from our previous research about the regulation and compatibility of plant-fungal associations. This project promises fascinating discoveries into the intertwined past, present and future of plants, microbes and soils.More than 80% of plants today associate with soil-dwelling fungi called Glomeromycota, forming mutually beneficial partnerships known as arbuscular mycorrhizas (AM). These cooperative partnerships involve the transfer of plant sugars, produced through photosynthesis, to fungal partners in return for essential nutrients mined from minerals in the soil by the fungi. When the first rootless plants emerged from water onto dry land more the 475 million years ago, it is thought that cooperative fungi provided the nutrients that plants needed to grow on land. Recent research by members of the project team has shown that some of the most evolutionarily ancient plants on Earth, the liverworts, form partnerships with fungi that are probably more evolutionarily ancient than AM. These fungi are called Mucoromycotina. Our findings suggest that associations between liverworts and Mucoromycotina fungi may be ancestral to the mycorrhizal symbiosis, paving the way for the colonisation of the terrestrial environment by plants and the evolution of the intricate terrestrial ecosystems that we are familiar with today. It is equally possible that the earliest land plants actually associated with both Mucoromycotina and AM simultaneously, as some plants still do today. For more than 30 years there has been a focus on AM as the ancestral plant-fungal symbiosis but with our surprising recent discovery of an alternative globally widespread and ancient association, we have the unique opportunity and pressing need to understand a new biology with potentially myriad ramifications for life on Earth.By using cutting-edge and novel methodologies from different fields of science, our research will generate crucial insights into the functioning and compatibility of cooperation between both groups of fungi with several major groups of land plants. Our experiments will be carried out under different atmospheric CO2 concentrations, reflecting the changing CO2 concentrations on Earth through evolutionary time, providing exciting new insights into the structure, function and evolution of modern plant-fungal symbioses.Through a deeper mechanistic and evolutionary understanding of the interaction between CO2 and diverse soil fungi, our research expands into wider aspects of soil ecology, plant-soil processes, and may lead to more efficient conservation strategies (see Pathways to Impact document). Through examining the physiological responses of symbiosis through different groups of land plants, this research will aid understanding and prediction of responses of these systems to ongoing changes in atmospheric CO2 concentrations; important considerations within the NERC Climate System and Biodiversity strategies, and with major implications for food security and soil ecology. Looking further into the future, the techniques and hypotheses that we develop and test through this research are transferable to other economically-important symbioses within the plant kingdom, such as fungal diseases of crops and the use of mycorrhizas in crops for future sustainable agriculture.