Converts salicylic acid (SA) to 2,3-dihydroxybenzoic acid (2,3-DHBA) (By similarity). Suppressor of immunity. Regulates negatively defense associated genes expression (e.g. PR-1, PR-2, and PR-5) (PubMed:18248595, PubMed:25376907). Negative regulator of defense against Hyaloperonospora arabidopsidis (PubMed:25376907). (Microbial infection) Required for susceptibility to the downy mildew pathogen Hyaloperonospora arabidopsidis. (Microbial infection) Required for susceptibility to Pseudomonas syringae pv. tomato DC3000. (Microbial infection) Required for susceptibility to the oomycete Phytophthora capsici. H(+) + NADH + O2 + salicylate = 2,3-dihydroxybenzoate + H2O + NAD(+) Binds 1 Fe(2+) ion per subunit. Locally induced during infections with both compatible and incompatible Hyaloperonospora arabidopsidis isolates, specifically in cells containing haustoria or directly surrounding the intercellular hyphae (PubMed:18248595, PubMed:25376907). Induced by the salicylic acid analog BTH. Accumulates in constitutive defense mutants (e.g. sid2 and npr1 mutants) (PubMed:18248595). Accumulates upon infection with the downy mildew Hyaloperonospora arabidopsidis, the powdery mildew Erysiphe orontii, and the bacterium Pseudomonas syringae as well as salicylic acid (SA) treatment (PubMed:25376907). In the double mutant eds1-2 dmr6-1 and in dmr6-2, reduced susceptibility to the downy mildew pathogen Hyaloperonospora arabidopsidis (PubMed:15986928, PubMed:18248595, PubMed:25376907). Reduced hyphal growth due to immature haustoria, often with aberrant shapes (PubMed:15986928, PubMed:18248595). Reduced susceptibility to Pseudomonas syringae pv. tomato DC3000 and the oomycete Phytophthora capsici, associated with enhanced defense gene expression and elevated salicylic acid levels (PubMed:25376907). Normal susceptibility to P. syringae pv. tomato and Golovinomyces orontii (PubMed:15986928). Enhanced expression of a subset of defense-associated genes (PubMed:18248595). Belongs to the iron/ascorbate-dependent oxidoreductase family.