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

这个合作项目的总体目标是阐明与皮脂腺菌相关的内生细菌的作用。由于其对植物的有益影响，高度多样化的菌根真菌具有很高的生态和农业意义。Piriformospora indica是研究最深入的皮脂腺菌属物种，含有α变形菌根瘤菌辐射杆菌PABac-DSM。三方关联的稳定性、细菌在无性繁殖和真菌植物定植过程中的垂直传播得到了证实（Sharma et al. 2008）。进一步筛选其他种类的皮脂腺菌复合的皮脂腺菌，鉴定出3种与Paenibacillus， Acinetobacter和Rhodococcus物种特异性相关。基于内细菌与皮脂腺菌和植物宿主形成复杂的三方关系的发现，我们假设细菌至少在一定程度上是共生有益结果所必需的。这一观点得到了以下事实的支持：在大麦根上施用放射线杆菌可以促进植物生长并诱导抗性，这与接种籼稻弧菌后观察到的活性类似。内源性细菌的重要性也可以从迄今为止还不能从细菌中治愈的事实中推断出来。为了进一步阐明印度假单胞菌和内细菌相互作用的分子基础，以及内细菌在三方联系中的作用，我们将基于目前可获得的印度假单胞菌和放射杆菌的基因组，采用遗传、分子、生化、生物物理和结构等方法。与F. Schröder， BTI， Ithaca合作，我们将使用基于二维核磁共振光谱的代谢组学结合HPLC-MS分析来鉴定真菌或细菌释放的这些过程中涉及的小分子。除了阐明indica-Rhizobium模型中三方相互作用的机制外，我们还将鉴定Sebacinales P. williamsii和Sebacina vermifera MAFF305838中的内生细菌，表征它们与真菌宿主的相互作用，确定这种相互作用的稳定性，并表征它们对特定三方相互作用的贡献。此外，我们将在田间试验条件下进行试验，以评估内细菌的农艺潜力。由于Kämpfer， Kogel和Schröder实验室的部分互补专业知识，我们期望高度协同作用有助于阐明内源性细菌在皮脂腺菌共生中的作用。对细菌-真菌-植物相互作用机制的基础研究将最终导致对共生关系及其如何对作物植物产生有益作用的更深入了解。该项目的结果将使我们能够评估内生细菌和/或其代谢物在植物保护方面的农艺潜力。

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.