The genetic architecture of the adaptive potential of Arabidopsis thaliana in response to Pseudomonas syringae strains isolated from south‐west France

Phytopathogens are a threat for global food production and security. Emergence or re‐emergence of plant pathogens is highly dependent on the environmental conditions affecting pathogen spread and survival. Under climate change, a geographic expansion of pathogen distribution poleward has been observed, potentially resulting in disease outbreaks on crops and wild plants. Therefore, estimating the adaptive potential of plants to novel epidemics and describing the underlying genetic architecture is a primary need to propose agricultural management strategies reducing pathogen outbreaks and to breed novel plant cultivars adapted to pathogens that might spread under climate change. To address this challenge, we inoculated Pseudomonas syringae strains isolated from Arabidopsis thaliana populations from south‐west of France on the highly genetically polymorphic TOU‐A A . thaliana population from north‐east France. While no adaptive potential was identified in response to most P . syringae strains, the TOU‐A population displayed a variable disease response to the JACO‐CL strain belonging to the P . syringae phylogroup 7 (PG7). This strain carried a reduced type III secretion system (T3SS) characteristic of the PG7 as well as flexible genomic traits and potential novel effectors. Genome‐wide association mapping on 192 TOU‐A accessions revealed a polygenic architecture of disease response to JACO‐CL. The main quantitative trait locus (QTL) region encompasses two R genes and the AT5G18310 gene encoding ubiquitin hydrolase, a target of the AvrRpt2 P . syringae effector. Altogether, our results pave the way for a better understanding of the genetic and molecular basis of the adaptive potential in an ecologically relevant A . thaliana – P . syringae pathosystem.