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

根瘤菌科植物（农杆菌）引起的冠瘿病是一种广泛存在且具有重要经济意义的植物病害，影响着许多农作物。农杆菌携带肿瘤诱导（Ti）质粒，对致病性至关重要，但也赋予肿瘤特异性代谢物opines的利用。我们最近解决了杜鹃花冠瘿病的病因学。在这方面，发现了一组新的致瘤根瘤菌，它似乎含有一种新型的钛质粒。杜鹃花的树冠瘿瘤中也存在携带特异性阿片分解代谢（OC）质粒的非致瘤性农杆菌。本项目旨在通过培养依赖和独立两种方法，进一步破译杜鹃花冠瘿瘤的细菌致病组，阐明优势菌群的基因组和质粒编码多样性和功能。杜鹃花冠瘿病也将作为研究肿瘤中种间相互作用生态学和动力学的模型。为此，将以番茄（试验植物）和杜鹃花（原寄主植物）进行温室试验。植物将接种致瘤性根瘤菌或非致病性农杆菌，以及以不同比例混合这两种细菌。接种菌株将在不同时间点通过核酸和显微镜方法进行监测。通过这种方式，可以验证致瘤性根瘤菌或非致病性农杆菌系统定植于接种过的植物并与肿瘤组织密切共定位的假设。进一步假设它们在冠瘿瘤的病理组中稳定共存。因此，假定病原体的种群维持在多物种群落中，不会被非致病性的阿片分解代谢细菌所淘汰。此外，该项目的目的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瘤病理组的组成、演替和定植的机制。同时也将为改进现有的冠瘿病治疗方法和探索新的治疗方法提供必要的依据。

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.