The Arabidopsis oxygenases DOWNY MILDEW RESISTANT 6 and DMR6-LIKE OXYGENASE 1 negatively regulate immunity by hydroxylation of salicylic acid
N. LUDWIG (1), J. Elberse (1), T. Zeilmaker (1), C. Böttcher (2), A. Melquiond (1), G. Van den Ackerveken (1) (1) Utrecht University, Netherlands; (2) Julius-Kühn Institut, Germany

Control of plant immune responses is important to regulate the balance between growth and defense. We previously found that Arabidopsis DOWNY MILDEW RESISTANT 6 (DMR6) and its paralogue DMR6-LIKE OXYGENASE 1 (DLO1) act as negative regulators of immunity. dmr6 mutants, and to a lesser extent dlo1 mutants, have increased levels of salicylic acid (SA), and are resistant to Hyaloperonospora arabidopsidis, Pseudomonas syringae and Phytophthora capsici. The dmr6 dlo1 double mutant has extremely high levels of SA, resulting in severe growth reduction. DMR6 and DLO1 act redundantly to maintain low SA levels in healthy plants and to control over-activation of SA-dependent defense. DLO1 is identical to the SA 3-hydroxylase (S3H) that was found to regulate SA levels during senescence (Zhang et al., PNAS 2013). Metabolite analysis of mutants and overexpression lines shows that DMR6 acts as SA 5-hydroxylase that oxygenates SA to 2,5-dihydroxy benzoic acid. The different phenotypes of the dmr6 and dlo1 single mutants could be caused by the position of hydroxylation on SA, or by the localization of DMR6/DLO1 expression. Promoter-swaps between DLO1 and DMR6 indicate that the difference in activity is determined by the promoter and not the coding sequence, suggesting that 3- and 5-hydroxylation of SA are equally effective in negative regulation of immunity.  We conclude that DMR6 and DLO1 control activated plant immunity in a tissue-specific manner by lowering SA levels through hydroxylation.

Abstract Number: P16-459
Session Type: Poster