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Poster

Session: Session 2 Presenting Authors at Posters (Evens)

P-132 - Inactivation of a Type VI effector of Ralstonia pseudosolanacearum enhances its proliferation in Mimosa pudica nodules during its experimental evolution as a legume symbiont

Thursday, July 17, 2025
13:30 - 15:15  
Location: Confex Hall 3
Effector Interference Mechanisms
Evolution has enabled certain bacteria to establish diverse associations with eukaryotes, ranging from parasitism to mutualism. These lifestyle transitions can occur through the horizontal acquisition of new genes as well as through changes in the expression or inactivation of endogenous genes. In order to investigate the molecular mechanisms driving the emergence of rhizobia, the phytopathogenic bacterium Ralstonia pseudosolanacearum was experimentally evolved into a Mimosa pudica symbiont. This was achieved by transferring symbiotic genes from the natural symbiont Cupriavidus taiwanensis and subjecting the resulting strain to repeated cycles of nodulation. Nodulation and intracellular infection were rapidly acquired and then strongly improved over the course of this experiment. Among the mutations contributing to this adaptive process, a missense mutation in a Type VI effector was found to enhance the bacterial proliferation in nodules while strongly reducing necrosis. We have shown that the mutated form of this effector is still secreted in vitro and that a deletion of this effector has a similar symbiotic phenotype, indicating that the mutation confers a loss of function of the protein. The absence of immunity gene in the vicinity of the gene encoding this effector, along with its 3D structure and preliminary data, suggest that this effector is an ADP ribosyl transferase targeting eukaryotic components. However, this hypothesis requires further experimental validation.