Communication in the tripartite Sebacinalean root symbiosis: the role of endomycotic bacteria

该合作项目的总体目标是阐明内生真菌与Sebacinalean真菌的作用。由于它们对植物的有益影响，高度多样的Sebacinales目的菌根真菌具有很高的生态和农业意义。Piriformospora indica是研究最深入的Sebacinalean物种，含有Alphaproteobacterium Rhizobium radiobium PABac-DSM。显示了三方联合的稳定性、无性真菌繁殖期间细菌的垂直传播和真菌植物定殖（Sharma等人，2008）。进一步筛选的其他物种的Sebacinales的Sebacina vermifera复杂的内生真菌细菌确定了三个物种特异性协会与类芽孢杆菌，不动杆菌，红球菌属物种。基于内细菌与Sebacinalean真菌和植物宿主形成复杂的三方关联的发现，我们假设细菌至少部分地是共生的有益结果所需的。这一观点得到了以下事实的支持：自由生活的R。辐射促进植物生长和诱导抗性，当应用于大麦根时，使人联想到接种P. indica后观察到的活性。为了进一步阐明P. indica和内生细菌相互作用的分子基础以及内生细菌在三方联合中的作用，我们将采用遗传学、分子生物学、生物化学、生物物理学和结构学等方法，以P. indica和R.辐射与F. Schröder，BTI，Ithaca，我们将使用基于二维NMR光谱的代谢组学结合HPLC-MS分析来识别参与真菌或细菌释放的这些过程的小分子。除了阐明P. indica-Rhizobium模型中三方缔合的机制之外，我们还将鉴定Sebacinales P. wilmurisii和Sebacina vermifera MAFF 305838中的内生真菌细菌，表征它们与真菌宿主的相互作用，确定缔合的稳定性，并表征它们对特定三方相互作用的贡献。此外，我们还将在田间试验条件下进行实验，以评估内生细菌的农学潜力。由于Kämpfer、Kogel和Schröder实验室的专业知识部分互补，我们预计将产生高度的协同效应，有助于阐明内生细菌在Sebacinalean共生中的作用。对细菌-真菌-植物互作机制的基础研究将有助于更深入地了解共生关系及其对作物的有益作用。该项目的结果将使我们能够评估内生真菌细菌和/或其代谢产物用于植物保护的农学潜力。

The overall goal of this collaborative project is to elucidate the role of endomycotic bacteria association with Sebacinalean fungi. Due to their beneficial impact on plants, highly diverse mycorrhizal fungi of the order Sebacinales have a high ecological and agricultural significance. Piriformospora indica, the most intensively studied Sebacinalean species, contains the Alphaproteobacterium Rhizobium radiobacter PABac-DSM. The stability of the tripartite association, the vertical transmission of bacteria during asexual fungal reproduction and fungal plant colonization, were shown (Sharma et al. 2008). Further screening for endomycotic bacteria in other species of the Sebacina vermifera complex of the Sebacinales identified three species-specific associations with Paenibacillus, Acinetobacter, and Rhodococcus species. Based on the finding that endobacteria form intricate tripartite association with Sebacinalean fungi and the plant hosts we hypothesize that bacteria are at least partly required for the beneficial outcome of the symbiosis. This view is supported by the fact that the free-living R. radiobacter mediates plant growth promotion and induced resistance when applied to barley roots reminiscent to activities observed after inoculation with P. indica. Significance of endobacteria is also inferred by the fact that Sebacinalean fungi could not be cured from bacteria so far.To further elucidate the molecular basis of the interaction of P. indica and endobacteria and the role of the endobacteria in the tripartite association, we will employ genetic, molecular, biochemical, biophysical, and structural methods - based on the now accessible genomes of P. indica and R. radiobacter. In cooperation with F. Schröder, BTI, Ithaca, we will use 2-dimentional NMR spectroscopy-based metabolomics combined with HPLC-MS analysis to identify small molecules involved in those processes released either by the fungi or bacteria. In addition to elucidating the mechanisms of the tripartite association in the P. indica-Rhizobium model, we will identify endomycotic bacteria in the Sebacinales P. williamsii and Sebacina vermifera MAFF305838, characterize their interaction with the fungal host, determine the stability of the association, and characterize their contribution to the specific tripartite interaction. Furthermore, we will conduct experiments under field test conditions to assess the agronomic potential of endobacteria.Due to the partly complementary expertise of Kämpfer, Kogel, and Schröder labs we expect a high synergism facilitating efforts to elucidate the role of endobacteria in the Sebacinalean symbiosis. Fundamental research on mechanism of the bacterial-fungal-plant interaction will eventually lead to a deeper understanding of the symbiosis and how it exerts beneficial activities on crop plants. Results from this project will enable us to assess the agronomic potential of endomycotic bacteria and/or their metabolites for plant protection.