Cold priming on pathogen susceptibility in the Arabidopsis eds1 mutant background requires a functional stromal Ascorbate Peroxidase .

24 h cold exposure (4°C) is sufficient to reduce pathogen susceptibility in Arabidopsis thaliana against the virulent Pseudomonas syringae pv. tomato ( Pst ) strain even when the infection occurs five days later. This priming effect is independent of the immune regulator Enhanced Disease Susceptibility 1 (EDS1) and can be observed in the immune-compromised eds1-2 null mutant. In contrast, cold priming-reduced Pst susceptibility is strongly impaired in knock-out lines of the stromal and thylakoid ascorbate peroxidases (sAPX/tAPX) highlighting their relevance for abiotic stress-related increased immune resilience. Here, we extended our analysis by generating an eds1 sapx double mutant. eds1 sapx showed eds1 -like resistance and susceptibility phenotypes against Pst strains containing the effectors avrRPM1 and avrRPS4. In comparison to eds1-2 , susceptibility against the wildtype Pst strain was constitutively enhanced in eds1 sapx . Although a prior cold priming exposure resulted in reduced Pst titers in eds1-2 , it did not alter Pst resistance in eds1 sapx . This demonstrates that the genetic sAPX requirement for cold priming of basal plant immunity applies also to an eds1 null mutant background.