Developmental and genetic dynamics of ambrosia beetle-fungal partner symbioses

仙甲虫在树上出没，它们在树皮上挖洞产卵。这些甲虫的独特之处在于它们也含有真菌，这些真菌生长在树的组织上，作为它们的食物来源。其中一些真菌会感染树木，在一些情况下会导致宿主树木在感染后的几个月内死亡。这些甲虫及其致病真菌分布在世界各地，对林业和自然生态系统构成重大威胁。然而，目前还没有研究任何神仙甲虫-真菌伴侣配对的遗传模型。本研究将以木耳甲虫-月桂枯萎病病原真菌（Harringtonia lauricola）为模型。原始甲虫和真菌都是入侵美国的，并迅速蔓延到整个国家的东南部。甲虫把真菌带到树上，真菌能够杀死原本健康的树木。有超过500种不同的树木被甲虫作为宿主，包括沼泽湾、红枣、黄樟和农业上重要的鳄梨作物，唯一的处理方法是砍伐和燃烧树木。在这个项目中，我们将研究甲虫如何庇护它的真菌伙伴的动力学和遗传学，包括甲虫如何选择，促进真菌的生长，并将真菌从宿主树带到宿主树。这些数据可以提供基础信息，最终可以用来帮助阻止这些树木病原体的传播。此外，该项目还将为高中生、本科生、研究生和博士后提供真菌生物学、疾病、共生和进化过程方面的培训和推广机会。在与佛罗里达大学的合作项目中，研究者将为高中教师和公众开发有关真菌-昆虫共生的教育材料。昆虫-真菌的共生关系在自然界中广泛存在，而神仙甲虫-真菌的相互作用代表了已知的最古老和最成功的共生关系。这种真菌是甲虫唯一的营养来源，甲虫在树上挖洞，形成洞穴，在那里生长，“种植”真菌作为食物。这些甲虫已经进化出专门的结构（菌丝）来容纳、运输和传播真菌。这些真菌和甲虫在整个进化史上共同适应了共生的生活方式，包括独立进化的不同类型的菌丝体，这些菌丝体容纳了不同的真菌共生体。这种真菌是一种极具破坏性的树木病原体，影响牛油果和其他樟科植物，仅在美国就杀死了3亿棵树。lauricola是其原始入侵（美国）甲虫载体（Xyleborus glabratus）的共生伙伴，现在可能已经传播到本土甲虫物种。我们将探讨月桂花和木甲之间关系的发育和遗传机制。该项目将使用细胞和遗传方法来测试有关共生关系的特定假设。我们将:(1)探索菌丝定植的细胞动力学，包括使用微生物学和细胞（如显微镜）方法研究菌丝的选择、持续/维持、更新和竞争；(2)确定介导真菌共生的遗传机制，例如，哪些真菌基因/网络对菌丝的定植和适应度很重要；真菌在菌丝定植期间的转录组学，以帮助定义导致真菌-菌丝共生的进化过程。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Ambrosia beetles infest trees, where they dig into the bark to lay their eggs. These beetles are unique in that they also harbor fungi that act as their food source which grows on the tree tissues. Some of these fungi can then infect the tree and in several cases can result in the death of host trees within months of infection. These beetles and their pathogenic fungi occur worldwide and pose a significant threat to forestry and natural ecosystems. However, no genetic models for the study of any ambrosia beetle-fungal partner pairings are available. This proposal will use the Xyloborus beetle-laurel wilt pathogenic fungus (Harringtonia lauricola) as a model. Both the original beetle and the fungus are invasive to the United States and are rapidly spreading throughout the Southeastern part of the country. The beetle carries the fungus to trees, where the fungus is capable of killing otherwise healthy trees. There are over 500 different species of trees that the beetle uses as a host including swampbay, redbay, sassafras, and the agriculturally important crop of avocado, where the only treatment is to cut and burn the trees. In this project, we will study the dynamics and genetics of how the beetle harbors its fungal partner, including how the beetle chooses, promotes the growth of, and carries the fungus from host tree to host tree. These data can provide foundational information that can ultimately be used to help stop the spread of these tree pathogens. In addition, the project will provide opportunities for training and outreach to high school, undergraduate, graduate, and postdoctoral students on fungal biology, disease, symbioses and evolutionary processes. In partnership with programs at University of Florida, the investigator will develop educational material for the high school teachers and the general public on fungal-insect symbioses. Insect-fungal mutualisms are widespread in nature and ambrosia beetle-fungal interactions represent some of the oldest and most successful symbioses known. The fungus serves as the sole source of nutrition for the beetles that burrow into trees to form galleries where they grow and “farm” the fungus for food. These beetles have evolved specialized structures (mycangia) that house, transport and disseminate the fungus. These fungi and beetles have co-adapted to symbiotic lifestyles throughout evolutionary history and include independent evolutions of different types of mycangia that house different fungal symbionts. The fungus, Harringtonia lauricola is a highly destructive tree pathogen affecting avocado and other members of the Lauraceae family and has killed 300 million trees in the US alone. H. lauricola is the mutualistic partner to its original invasive (to the US) beetle carrier (Xyleborus glabratus) and may have now spread to indigenous beetle species. We will investigate the developmental and genetic mechanisms which underlie the relationship between H. lauricola and Xyleborus beetles. The project will use cellular and genetic approaches to test specific hypotheses concerning symbiotic association. We will: (1) probe the cellular dynamics of mycangial colonization, including investigating selection, persistence/maintenance, turnover, and competition in the mycangia using microbiological and cellular (e.g., microscopic) methods, (2) identify genetic mechanisms that mediate fungal symbioses, e.g., what fungal genes/network are important for colonization and fitness within the mycangia, and (3) construct gene expression profiles (i.e., transcriptomics) of the fungus during mycangial colonization to help define the evolutionary processes that has led to fungal-mycangial symbioses.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.