Stone Lauren B L, Bidochka Michael J
Department of Biological Sciences, Brock University, St. Catharines, ON, L2S 3A1, Canada.
Appl Microbiol Biotechnol. 2020 Dec;104(23):9935-9945. doi: 10.1007/s00253-020-10968-3. Epub 2020 Oct 21.
The genus Metarhizium is comprised of a diverse group of common soil fungi that exhibit multifunctional lifestyles with varying degrees of saprotrophic, endophytic, and insect pathogenic modes of nutrient acquisition. The transcriptome of these species is modulated to reflect immediate needs of the fungus and availability of resources-a form of transcriptional plasticity that allows for physiological adaptation to environments with diverse and dynamic exploitable nutrient sources. In this review, we discuss the endophytic, insect pathogenic lifestyles of Metarhizium spp., including their symbiotic interface, origins, and evolution, and agricultural applications. Isotope labeling experiments have demonstrated that a mutually beneficial exchange of limiting nutrients occurs between the fungus and its host plant, with nitrogen derived via insect pathogenesis being translocated from Metarhizium to host plants in exchange for fixed carbon in the form of photosynthate. Thus, the endophytic and entomopathogenic abilities of Metarhizium spp. are not exclusive of one another, but rather are interdependent and reciprocal in nature. Although endophytic, insect pathogenic fungi (EIPF) could certainly have evolved from insect pathogenic fungi, phylogenomic evidence indicates that this genus is more closely related to plant-associated fungi than animal pathogens, suggesting that Metarhizium evolved from a lineage of plant symbionts, which subsequently acquired genes for insect pathogenesis. Entomopathogenicity may have been an adaptive trait, allowing for procurement of insect-derived nitrogen that could be translocated to host plants and bartered for fixed carbon, thereby improving the stability of fungal-plant symbioses. Given their ability to simultaneously parasitize soil insects, including a number of pests of agriculturally important crops, as well as promote plant health, growth, and productivity, Metarhizium spp. are considered promising alternatives to the chemical pesticides and fertilizers that have wreaked havoc on the health and integrity of ecosystems. KEY POINTS: • Metarhizium is a fungus that is an insect pathogen as well as a plant symbiont. • The genus Metarhizium has specialist and generalist insect pathogens. • Metarhizium is phylogenetically most closely related to plant endophytes.
绿僵菌属由多种常见的土壤真菌组成，这些真菌呈现出多功能的生活方式，具有不同程度的腐生、内生和昆虫致病营养获取模式。这些物种的转录组受到调控，以反映真菌的即时需求和资源可用性——这是一种转录可塑性形式，使真菌能够在具有多样且动态可利用营养源的环境中实现生理适应。在本综述中，我们讨论了绿僵菌属的内生、昆虫致病性生活方式，包括它们的共生界面、起源和进化以及农业应用。同位素标记实验表明，真菌与其宿主植物之间发生了有限养分的互利交换，通过昆虫致病作用获得的氮从绿僵菌转移到宿主植物，以换取光合产物形式的固定碳。因此，绿僵菌属的内生和昆虫致病能力并非相互排斥，而是在本质上相互依存且相互作用。虽然内生昆虫致病真菌（EIPF）肯定可能从昆虫致病真菌进化而来，但系统基因组学证据表明，该属与植物相关真菌的关系比动物病原体更为密切，这表明绿僵菌是从植物共生菌的一个谱系进化而来的，随后获得了昆虫致病基因。昆虫致病性可能是一种适应性特征，使得能够获取可转移到宿主植物并交换固定碳的昆虫源氮，从而提高真菌 - 植物共生关系的稳定性。鉴于绿僵菌属能够同时寄生土壤昆虫，包括许多重要农作物的害虫，还能促进植物健康、生长和生产力，它们被认为是对严重破坏生态系统健康和完整性的化学农药和化肥的有前途的替代品。要点：• 绿僵菌是一种既是昆虫病原体又是植物共生体的真菌。• 绿僵菌属有专性和兼性昆虫病原体。• 绿僵菌在系统发育上与植物内生菌关系最为密切。
