The making of a pathogen : How Xanthomonas adapts to plant environments – XBOX

This project propose to combine in planta transcriptomic analyses and high-throughput RB-TnSeq screens to identify bacterial determinants of fitness in different in vitro and in planta conditions.
To determine the genetics of adaptation of Xcc at all stages of cauliflower infection in-depth RB-TnSeq screening will be performed in planta or in planta-related conditions. RB-TnSeq measures the relative abundance of a complex transposon-mutants library of Xcc before/after inoculation in the different plant compartments Such RB-TnSeq approach will identify genes that contribute quantitatively to i) growth in a number of poor media related to plant fluids, ii) to pathogenicity and iii) to adaptation to plant environment such as xylem sap, hydathodes and mesophyll tissue.
To capture bacterial transcriptomes at different steps of infectionc and to correlate fitness results with changes in transcriptional reprogramming during infection, transcriptome of Xcc will be determined throughout the infection cycle by RNA-seq in the same conditions described for RB-TnSeq experiments. Comparative transcriptomic analyses will enable the identification of genes and pathways potentially important for the pathogenicity, fitness and adaptation of Xcc to the leaf, in the hydathode, in the mesophyll and in xylem sap.

The physiological state as well as the adaptation strategy of Xcc to the first endophytic tissue encountered, the hydathode, was determined by transcriptomic and genetic analysis and is the subject of a publication submitted in the «Molecular Plant Pathology” journal.
On the other hand, 180 genes involved in the bacterial fitness of Xcc within the hydathode have been identified. Among them, the characterization of new virulence factors was carried out. All of these results are the subject of a publication in progress.

This project is of an Economic relevance since Xanthomonas campestris belongs to the «Top 10» phytopathogenic bacteria because of its agronomic and academic importance. This ambitious long-term project will undoubtedly extend the knowledge on pathways important for Xcc fitness and plant adaptation at different steps of infection. Since Xcc is a model vascular pathogen, results obtained in the frame of the project should be transposable to other vascular pathogen such as the closelyrelated xylem-limited pathogen Xylella fastidiosa or Ralstonia solanacearum.
As long-term perspective, the project will identify essential pathogenicity traits allowing development of systems and synthetic biology projects on Xcc pathogenicity. Indeed, Omics data can be used to generate metabolic network models that quantitatively capture the cellular metabolism and predict phenotypes. This kind of models could be exploited to better understand pathogenicity and hostpathogen interactions to higher levels of complexity and predict what would be the impacts of different biotic and abiotic changes on these interactions.

Un article soumis à «Molecular Plant Pathology« journal

Ability of a microorganism to cause disease is based on evasion of host defenses and on a finely tuned virulence program needed to adapt to host environments. My research project focuses on the identification and characterization of genetic determinants of bacterial fitness during infection of Brassica crops by the bacterium Xanthomonas campestris (Xc), the causal agent of black rot disease. Through in planta -omic analyzes, the XBOX project will provide a snapshot of the physiological and transcriptomic status of Xc during infection and will lead to (i) the characterization of new genes of unknown function involved in fitness in planta; (ii) the characterization of regulators associated with different stages of transcriptomic reprogramming; (iii) the identification of important pathways for adaptation to different plant tissues. This project will undoubtedly lead to knowledge breakthroughs on this pathosystem and will open ways for the development of new strategies to control epiphytic and vascular pathogens on cultivated crops.