Interactions in the bacterial pathobiome associated with crown gall disease: coexistence or competition?

根癌病是由根瘤菌科的农杆菌引起的一种广泛存在的重要的植物病害。农杆菌携带的肿瘤诱导（Ti）的质粒，是致病性所必需的，但也赋予利用肿瘤特异性代谢产物称为opines.We最近解决了杜鹃冠瘿病的病因。在这方面，一个新的组的致瘤根瘤菌的物种，似乎窝藏一种新型的Ti质粒被发现。杜鹃花上的冠瘿瘤也被非致瘤性农杆菌所占据。携带特定的阿片分解代谢（OC）质粒。本项目旨在通过培养依赖和非培养依赖两种方法，进一步破译杜鹃花冠瘿瘤的细菌致病生物组，阐明优势细菌种群的基因组和质粒编码的多样性和功能，并以杜鹃花冠瘿病为模型，研究肿瘤中种间相互作用的生态学和动力学。为此，将进行番茄（试验植物）和杜鹃花（原始宿主植物）的温室实验。将植物接种致瘤根瘤菌属或非致病性农杆菌属，以及这两种细菌以不同比例混合。将在不同时间点使用基于核酸的方法和显微镜方法监测接种菌株。以这种方式，将测试致瘤性根瘤菌属或非致病性农杆菌属系统地定殖接种的植物并在肿瘤组织中紧密共定位的假设。进一步假设它们稳定地共存于冠瘿肿瘤的病理生物组内。因此，它是假设的病原体的人口是保持在多物种社区，而不是由非致病性的冠醚分解代谢细菌的竞争。此外，本项目的目标是研究种间相互作用对疾病发展的影响，该项目结合了植物病理学和微生物生态学的不同先进方法，将有助于更好地了解冠瘿肿瘤病原生物组的组成，演替和定殖机制。同时，也为改进现有的冠瘿病防治方法和探索新的防治方法提供了必要的依据。

Crown gall caused by tumorigenic Rhizobiaceae species (agrobacteria) is a widespread and economically important plant disease affecting numerous agricultural crops. Agrobacteria carry a tumor-inducing (Ti) plasmid that is essential for pathogenicity, but also confer utilization of tumor-specific metabolites called opines.We have recently resolved etiology of the crown gall disease of rhododendron. In this respect, a novel group of tumorigenic Rhizobium sp. that seems to harbor a new type of Ti plasmid was discovered. Crown gall tumors on rhododendron were also inhabited by nontumorigenic Agrobacterium spp. carrying a specific opine-catabolic (OC) plasmid. This project aims to further decipher the bacterial pathobiome of crown gall tumors of rhododendron and to elucidate the genome- and plasmid-encoded diversity and functions of the dominant bacterial populations by using both cultivation-dependent and -independent methods.Crown gall disease of rhododendron will be also used as a model to study the ecology and dynamics of interspecies interactions in tumors. For this purpose, greenhouse experiments with tomato (test plant) and rhododendron (original host plant) will be performed. Plants will be inoculated with either tumorigenic Rhizobium sp. or nonpathogenic Agrobacterium sp., as well as with both of these bacteria mixed in different ratios. Inoculant strains will be monitored at different time points by using nucleic acid-based and microscopy methods. In this way, the hypothesis that tumorigenic Rhizobium sp. or nonpathogenic Agrobacterium sp. systemically colonize inoculated plants and are intimately co-localized in tumor tissue will be tested. It is further hypothesized that they stably coexist within the pathobiome of crown gall tumors. Consequently, it is assumed that the population of the pathogen is maintained in the multispecies community and not outcompeted by nonpathogenic opine-catabolizing bacteria. Moreover, the objective of this project is to investigate the effects of the interspecies interactions on disease development.The project combines different advanced approaches from plant pathology and microbial ecology and will contribute to the better mechanistic understanding of the composition, succession and colonization of the pathobiome of crown gall tumors. Moreover, it will also provide an essential basis for the improvement of existing and the exploration of new approaches for management of crown gall disease.