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

• Applicant: Dr. Nemanja Kuzmanovic
• Subject Area: Plant Breeding and Plant Pathology
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 429677233

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.

• DFG Programme: Research Grants