Zaman Rashaduz, May Courtney, Ullah Aziz, Erbilgin Nadir
Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2E3, Canada.
Metabolites. 2023 Feb 6;13(2):239. doi: 10.3390/metabo13020239.
Bark beetles maintain symbiotic associations with a diversity of microbial organisms, including ophiostomatoid fungi. Studies have frequently reported the role of ophiostomatoid fungi in bark beetle biology, but how fungal symbionts interact with host chemical defenses over time is needed. We first investigated how inoculations by three fungal symbionts of mountain pine beetle affect the terpene chemistry of live lodgepole pine trees. We then conducted a complimentary laboratory experiment specifically measuring the host metabolite degradation by fungi and collected the fungal organic volatiles following inoculations with the same fungal species on lodgepole pine logs. In both experiments, we analyzed the infected tissues for their terpene chemistry. Additionally, we conducted an olfactometer assay to determine whether adult beetles respond to the volatile organic chemicals emitted from each of the three fungal species. We found that all fungi upregulated terpenes as early as two weeks after inoculations. Similarly, oxygenated monoterpene concentrations also increased by several folds (only in logs). A large majority of beetles tested showed a strong attraction to two fungal species, whereas the other fungus repelled the beetles. Together this study shows that fungal symbionts can alter host defense chemistry, assist beetles in overcoming metabolite toxicity, and provide possible chemical cues for bark beetle attraction.
树皮甲虫与多种微生物保持共生关系，包括长喙壳菌。研究经常报道长喙壳菌在树皮甲虫生物学中的作用，但随着时间的推移，真菌共生体如何与宿主化学防御相互作用仍有待研究。我们首先研究了山地松甲虫的三种真菌共生体接种如何影响活的黑松的萜烯化学。然后，我们进行了一项补充实验室实验，专门测量真菌对宿主代谢物的降解，并在黑松原木上接种相同真菌物种后收集真菌有机挥发物。在这两个实验中，我们分析了受感染组织的萜烯化学。此外，我们进行了嗅觉测定，以确定成年甲虫是否对三种真菌物种各自释放的挥发性有机化合物有反应。我们发现，所有真菌在接种后两周就上调了萜烯含量。同样，含氧单萜浓度也增加了几倍（仅在原木中）。绝大多数测试的甲虫对两种真菌表现出强烈的吸引力，而另一种真菌则排斥甲虫。这项研究共同表明，真菌共生体可以改变宿主防御化学，帮助甲虫克服代谢物毒性，并为树皮甲虫的吸引提供可能的化学线索。
