DISSERTATION RESEARCH: Are ectomycorrhizal fungi acquiring resources made available by the activity of extracellular enzymes secreted by saprotrophs?

越来越明显的是，植物的健康，就像人类的健康一样，在很大程度上取决于它们与微生物的密切相互作用。 这个隐藏的微生物世界影响着土壤中碳储存的关键过程，这反过来又稳定了土壤以防止侵蚀，并提供了支持植物生长的营养和水分来源。 许多植物物种与生长在其根部周围的某些类型的真菌形成联系。 这些被称为外生菌根真菌（EMF）的真菌参与共生，将营养素交换为糖，从而促进土壤碳的地下储存。 利用来自宿主植物的碳作为燃料，EMF从根表面分支以形成网络并增加用于营养吸收的表面积。 然而，当植物的碳供应有限时，EMF可能会与自由生活（非共生）的微生物竞争养分和碳。 或者，EMF也可以“欺骗”或捕获由群落中其他微生物的作用产生的降解产物，而不是直接竞争。 该项目支持正在进行的论文研究，以确定EMF是否可能使用另一种生物体释放的植物降解产物（即“作弊”）。 本研究结果将有助于更好地了解真菌在植物凋落物降解中的作用。 研究结果还将改善对气候变化对分解影响的预测。 这项研究的更广泛的影响包括培养一名博士生，以及培养几名本科生的机会。微生物物种在其分解难降解植物聚合物（如纤维素和木质素）成易代谢单体的能力方面各不相同。 微生物基因组中胞外酶（ECE）基因组合的多样性表明降解这些聚合物的能力不同。 该项目的初步测试利用了在受控微观世界中生长的模式生物，从而受益于受控的实验环境和可用于充分研究的物种的序列数据。 这些测试表明，EMF中的聚合物降解酶活性并不直接反映酶降解基因的存在。 目前的项目将通过元转录组学分析来支持初步结果，揭示EMF和自由生活的腐营养生物在基因表达水平上的竞争相互作用，并展示EMF如何在特定环境中优化它们的成功。研究人员将比较mRNA序列与全基因组序列，使用标准方法将每个序列读取映射到相应的基因组。这将允许量化在EMF中与其他微生物竞争并且没有来自宿主植物的碳供应的情况下表达的ECE基因。 这些基因表达的变化，加上生理数据，将使研究人员能够验证那些消耗聚合物降解产物的生物体是否也表达ECE基因（即，是否作弊）。 从这项研究中获得的知识将提高我们对EMF在分解中的作用的理解，并将其活动纳入碳循环模型。

It has become increasingly evident that the health of plants, like that of humans, depends largely on their close interaction with microbes. This hidden world of microbes influences processes critical to the storage of carbon in the soil, which in turn stabilizes the soil to prevent erosion, and provides a source of nutrients and water to support plant growth. Many plant species form associations with certain types of fungi that grow around their roots. These fungi, known as ectomycorrhizal fungi (EMF), engage in a symbiosis, exchanging nutrients for sugars, thereby promoting belowground storage of soil carbon. Using carbon from the host plant as fuel, EMF branch out from the root surface to form networks and improve surface area for nutrient uptake. However, when the carbon supply from the plant is limited, EMF may compete with free-living (non-symbiotic) microbes for both nutrients and carbon. Alternatively, instead of direct competition, EMF could also "cheat" or capture the degraded products generated by the action of other microbes in the community. This project supports ongoing dissertation research to establish whether EMF might use plant degradation products released by another organism (i.e. "cheat"). Results of this research will contribute to a better understanding of the role of fungi in plant litter degradation. The results will also improve predictions about the effects of climate change on decomposition. The broader impacts of this study include the training a doctoral student as well as opportunities for training of several undergraduate students.Microbial species vary in their ability to break down recalcitrant plant polymers, such as cellulose and lignin, into easily metabolized monomers. The diversity of gene combinations for extracellular enzymes (ECE) seen in microbial genomes points to a differential ability to degrade these polymers. The preliminary tests of this project leveraged model organisms grown in controlled microcosms, thereby profiting from a controlled experimental setting and sequence data available for well-studied species. These tests demonstrated that polymer-degrading enzyme activity in EMF is not directly reflective of the presence of enzyme-degrading genes. The current project will bolster the initial results via metatranscriptomic analyses, shed light on competitive interactions between EMF and free-living saprotrophs at the gene expression level, and show how EMF optimize their success in a particular environment. The researchers will be comparing mRNA sequences to full genome sequences, using standard methods to map each sequence read to a corresponding genome. This will allow for quantification of expressed ECE genes in EMF in competition with other microorganisms and without a carbon supply from a host plant. Shifts in expression of these genes, coupled with physiological data, will allow the researchers to verify whether those organisms that consume polymer degradation products are also expressing ECE genes (i.e., whether they are cheating). The knowledge gained from this research will enhance our understanding of the role of EMF in decomposition and to incorporate their activities in carbon cycling models.