MIP: Bacterial Endosymbionts of Phyllosphere Fungi:resolving the Endophyte/Saprophyte/Pathogen continuum on the Navajo Nation

内生真菌是生活在叶子等植物组织内而不引起疾病的真菌，存在于从北极到热带、从农田到原始森林的健康植物中。尽管长期以来被生物学家忽视，但内生菌现在因其巨大的多样性、它们在陆地植物所有谱系中的分布以及它们在调节植物应激和抗病原体防御中的生态作用而得到认识。该实验室从超过 8000 种以前未知的内生菌中提取，表明这些无害的共生体是复杂进化连续体的一部分，其特征是频繁且重复的进化转变（1）病原生活方式和内生生活方式之间，以及（2）从内生生活方式到腐养生活方式。这些观察结果提出了一个问题：哪些遗传、生态和进化因素允许真菌在独特的生态模式之间如此频繁和反复地切换？这项拟议的研究将检验一个普遍的假设，即生活在植物相关真菌中的新发现的细菌内共生体在驱动真菌宿主的“转换”方面发挥着重要的、以前被忽视的作用，因此是了解它们所栖息的真菌的生态模式的关键。这项研究将结合实地调查、系统发育分析和实验，以检查与楚斯卡山脉（亚利桑那州东北部生物丰富但研究不足的地区）内真菌、腐生菌和病原体相关的细菌内共生体的发生率、多样性、宿主亲和力、进化关系和生态重要性。这项工作的大部分将在纳瓦霍族保留地进行，并为戴恩学院的纳瓦霍本科生提供保留地研究培训。这项工作的智力价值在于确定哪些隐秘的细菌内共生体驱动不同真菌的表型，而这反过来又对其所栖息的植物的生态和进化都很重要。更广泛的影响包括 (1) 美洲原住民部落学院的课程开发，(2) 支持最多 30 名本科生（包括 18 名纳瓦霍学生）的指导研究，以及 (3) 支持两名女博士。真菌和细菌生态学、进化论和分类学的学生。

Fungal endophytes, fungi that live within plant tissues such as leaves without causing disease, occur in healthy plants from the Arctic to the tropics, and from agricultural fields to primary forests. Although long overlooked by biologists, endophytes are now being recognized for their tremendous diversity, their distribution across all lineages of land plants, and their ecological roles in mediating plant stress and antipathogen defense. Drawing from a collection of over 8000 previously unknown endophytes, this laboratory is showing that these harmless symbionts are part of a complex evolutionary continuum that features frequent and repeated evolutionary transitions (1) between pathogenic and endophytic lifestyles, and (2) from endophytic to saprotrophic lifestyles. These observations raise the question: what are the genetic, ecological, and evolutionary factors that permit such frequent and repeated switching among distinctive ecological modes in fungi? The proposed study will test the general hypothesis that newly discovered bacterial endosymbionts living within plant-associated fungi play a significant and previously overlooked role in driving the "switching" of their fungal hosts, and thus are key to understanding the ecological modes of the fungi they inhabit. This study will combine field surveys, phylogenetic analyses, and experiments to examine the incidence, diversity, host affinity, evolutionary relationships, and ecological importance of bacterial endosymbionts associated with fungal endophytes, saprotrophs, and pathogens in the Chuska Mountains, a biotically rich but understudied area in northeastern Arizona. Much of this work will be carried out on the Navajo Nation with on-reservation research training for Navajo undergraduates at Dine College. The intellectual merit of this work lies in determining which cryptic bacterial endosymbionts drive the phenotypes of diverse fungi, which in turn are important in both the ecology and evolution of the plants they inhabit. Broader impacts include (1) curriculum development at a Native American tribal college, (2) support for mentored research by up to 30 undergraduates, including 18 Navajo students and (3) support for two female Ph.D. students in fungal and bacterial ecology, evolution, and taxonomy.