Contrasting Salt Stress Concentrations and their Impact on Disease Susceptibility in Arabidopsis thaliana

Plants are constantly exposed to challenging environmental factors that can threaten their survival. Multiple environmental stressors often happen simultaneously, and plants have to prioritize certain responses, compromising their defenses against others. Abscisic acid (ABA), produced under osmotic stress, is known to inhibit the production of salicylic acid (SA), a key regulator of pathogen response. However, ABA is not the only hormone that regulates salt stress, and different concentrations of salt might impact the crosstalk between salt and immune response mechanisms differently. Further, leaf microbiome is known to be sensitive to the physiological changes of the leaf, but the effects of these changes on the salt and defense combined stress are still unknown. Using the plant-pathogen model system of Arabidopsis thaliana and Pseudomonas syringae pv. tomato strain DC3000 (Pst DC3000), we were able to quantify the negative effects of salt stress on the defense response against Pst DC3000. We also identified variations in the regulation of defense under high concentrations and low concentrations of salt. Although both concentrations of salt have a negative effect on immunity, the differences in the mechanisms involved pose the question of whether there is a one-size-fits-all solution to overcome this combined stress. In conclusion, our findings emphasize the complexity of the interplay between hormone regulation, microbiome composition, and osmoregulation in shaping the defense response during salt stress and provides insight on the molecular targets that could enhance plant resilience during combined stress.