Fight Club : the antagonistic behavior of Xanthomonas translucens secretion systems and its effect on barley

Details

Supervisors

Bragard, Claude ; Peduzzi, Chloé

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences et technologies de l'environnement, à finalité spécialisée

Abstract

The genus Xanthomonas comprises at least 27 species with the potential to infect over 400 plant species. Notably, Xanthomonas translucens is a pathogen causing Bacterial Leaf Streak, leading to significant damage in cereal fields annually. To thrive, this bacterium must navigate a diverse array of competitor bacteria and host plant defense mechanisms. Thus, X. translucens possesses an elaborate arsenal, including the Type 6 Secretion System (T6SS). Despite its discovery in Vibrio cholera and prevalence in various Gram-negative bacteria, the T6SS in Xanthomonas translucens remains underexplored, particularly in terms of interbacterial competition, effectors, and host resistance mechanisms. To investigate interbacterial competition, we employed a method involving the generation of mutants and reverse complementation to assess altered secretion system functions. Various genes from the i3*** and i4 clades of the T6SS in Xanthomonas translucens pv. undulosa were removed and confronted with different competitor bacteria, both qualitatively and quantitatively. These experiments highlighted the involvement of the Xtu T6SS-i4 gene cluster in interbacterial competition against Escherichia coli and Pseudomonas poae, while T6SS-i3 did not seem to play a role under these conditions. Growth curves of these mutants indicated a slight decrease in the fitness of X. translucens pv. undulosa upon the removal of the T6SS-i4 region, leading us to believe the presence of a gene with regulatory or growth-related functions. Subsequently, in silico analyses identified two neighboring genes in the Xanthomonas translucens pv. undulosa T6SS-i4 cluster as homologs of Vibrio cholerae vasX T6SS effector gene and its cognate immunity protein TsiV2. Two mutants were therefore planned. Unfortunately, attempts to characterize these genes through mutant generation were unsuccessful. Lastly, the pdTAL effector was used to introduce a mutation in a Xanthomonas translucens pv. translucens strain, activating the barley immunity gene rph3. This approach aimed to observe in planta reactions and elucidate the behavior of the rph3 gene but due to lack of time, the in planta assays could not be carried out during this work. This work supports previous results showing a role for X. translucens T6SS in interbacterial competition but also opens avenues for further research on Xanthomonas translucens secretion systems, some of which remain unrecognized.