Bacterial Endosymbionts of Endophytic Fungi: Diversity, Coevolution, and Ecological Roles.

生活在健康的植物组织中而不会引起疾病的真菌内生菌和真菌在所有主要的陆地植物谱系中都是已知的。这些不同但鲜为人知的共生体由于在感染周期的重要阶段宿主上没有疾病症状而结合在一起，在许多情况下对它们所栖息的植物有有利的影响(例如，对害虫的威慑)。最近的研究表明，许多植物伴生真菌都寄生在细菌内共生菌中，细菌内共生菌可以影响这些真菌的致病性。内生菌与植物病原菌关系密切，但可能使它们易于致病或无毒的进化、生态或遗传因素尚不清楚。在初步研究中，细菌内共生体被证明存在于表面上纯净的内生真菌培养物中，但这些细菌的多样性、分类群组成和生态作用从未被探索过。这项拟议的工作将利用一个超过8000个活体内生真菌培养物的独特文库来(1)确定细菌内共生菌在内生真菌中的出现频率；(2)比较内生共生菌和内生真菌的多样性、地理分布和寄主专一性；(3)通过实验评估细菌内共生菌在内生真菌和相关植物病原真菌中的生态作用。该项目将阐明细菌介导真菌毒力的方式，为研究真菌与植物的相互作用提供重要工具。这项研究的学术价值在于解开了植物-微生物共生中新发现的复杂程度，并捕捉到了内部共生菌的多样性，这些共生菌本身生活在一个超分化的共生微生物协会中。该项目将帮助培训一至三名本科生和一名研究生，特别侧重于培训传统上在科学界任职人数不足的群体中的个人。

Fungal endophytes and fungi that live within healthy plant tissues without causing disease are known from all major lineages of land plants. These diverse but little-known symbionts are united by the absence of disease symptoms on their hosts during a significant phase of the infection cycle, and in many cases have beneficial effects on the plants they inhabit (e.g., pest deterrence). Recent work has shown that many plant-associated fungi are inhabited by bacterial endosymbionts, which can influence pathogenicity of those fungi. Endophytes are closely related to plant pathogens, but the evolutionary, ecological, or genetic factors that may predispose them to pathogenicity or avirulence are unknown. In preliminary studies, bacterial endosymbionts were shown to be present in apparently pure cultures of endophytic fungi, but the diversity, taxon composition, and ecological roles of these bacteria have never been explored. The proposed work will take advantage of a unique library of over 8000 living endophyte cultures to (1) determine the frequency with which bacterial endosymbionts occur among endophytic fungi; (2) compare the diversity, geographic distribution, and host specificity of endosymbiotic bacteria with those of endophytic fungi; and (3) experimentally assess the ecological roles of bacterial endosymbionts in endophytic and related plant-pathogenic fungi. This project will shed light on the ways in which bacteria mediate virulence in fungi, providing an important tool in the study of fungal-plant interactions. The intellectual merit of this study lies in disentangling a newly discovered level of complexity in plant-microbe symbioses, and in capturing the diversity of endosymbionts that themselves live within a hyperdivese guild of symbiotic microbes. This project will contribute to the training of one to three undergraduates and one graduate student, with a special focus on training individuals from groups that are traditionally under-represented in the sciences.