P-276 - Temperature plays a decisive role in the ability of Pseudomonas syringae to trigger ETI and drives in planta bacterial growth dynamics

The P. syringae species complex has a very huge economic impact, causing diseases in many plant species. Substantial research effort is being invested to understand how effector repertoires could determine the host range of a given strain. Although a specific set of effectors is fundamental, it is not sufficient to guarantee a successful plant colonization. Indeed, environmental factors play a major role in the ability of P. syringae to secrete effectors efficiently. Recently, we showed that the inability of P. syringae pv. actinidiae to induce a hypersensitive response (HR) in A. thaliana is due to its inability to inject a recognized effector rather than its absence. We thus compared several P. syringae strains carrying a plasmid-borne avirulence gene for their ability to induce an HR in A. thaliana Col-0 at different temperatures. Moreover, the temperature-dependent growth dynamics of these strains were evaluated in different plant species. Overall, the results showed that the temperature influences bacterial growth dynamics in planta, although it does not fully correlate with their ability to activate the type three secretion system (T3SS). The differences observed among strains indicate that (i) a single strain can’t be considered as representative of the P. syringae complex, (ii) temperature affects bacterial fitness regardless of the host and (iii) the ability of bacteria to activate and use the T3SS is likely as important as possessing the right set of effectors.