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

植物在超过475 Ma的地球陆地上定居，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，共生真菌通过增加获得矿物养分的机会来换取光合作用固定的有机碳，从而促进了植物早期的陆地化。我们最近的发现对现存最早的陆地植物分化谱系的真菌共生体的身份、生物学和功能提出了质疑。我们的项目解决了这些基本的知识差距，包括我们之前关于植物-真菌联合的调节和兼容性的研究产生的关键新问题。该项目有望对植物、微生物和土壤相互交织的过去、现在和未来做出令人着迷的发现。今天，超过80%的植物与土壤真菌Glmer mycota联系在一起，形成了称为丛枝菌根(AM)的互惠伙伴关系。这些合作伙伴关系包括将通过光合作用产生的植物糖转移到真菌伙伴，以换取真菌从土壤中的矿物质中开采出的基本营养。4.75亿多年前，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。项目团队成员最近的研究表明，地球上一些进化最古老的植物--苔类植物--与可能比AM更古老的真菌形成了伙伴关系这些真菌被称为毛霉菌。我们的发现表明，地钱和毛霉菌之间的联系可能是菌根共生的祖先，为植物在陆地环境中的殖民和我们今天所熟悉的复杂陆地生态系统的进化铺平了道路。同样有可能的是，最早的陆地植物实际上同时与毛霉和AM联系在一起，就像今天一些植物仍然做的那样。30多年来，人们一直关注AM作为原始植物-真菌共生的问题，但随着我们最近令人惊讶地发现了另一种全球广泛存在的古老联系，我们有独特的机会和迫切的需求来了解一种新的生物学，这种新的生物学可能对地球上的生命产生无数的影响。通过使用来自不同科学领域的尖端和新颖的方法，我们的研究将产生关键的洞察力，以了解这两类真菌与几种主要陆地植物之间的合作的功能和兼容性。我们的实验将在不同的大气二氧化碳浓度下进行，反映地球上二氧化碳浓度随进化时间的变化，为现代植物-真菌共生生物的结构、功能和进化提供令人兴奋的新见解。通过对二氧化碳与不同土壤真菌之间相互作用的更深层次的机制和进化的理解，我们的研究扩展到土壤生态、植物-土壤过程的更广泛的方面，并可能导致更有效的保护策略(参见Path to Impact文档)。通过研究不同类型陆地植物共生的生理反应，这项研究将有助于理解和预测这些系统对大气二氧化碳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，以及对粮食安全和土壤生态的重大影响。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内的其他重要经济共生领域，例如作物的真菌疾病和在作物中使用菌根以实现未来的可持续农业。

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.