Dual and opposing roles of xanthine dehydrogenase in defense-associated reactive oxygen species metabolism in Arabidopsis
X. MA (1), W. Wang (2), F. Bittner (3) (1) University of Maryland, U.S.A.; (2) Sichuan Agricultural University, China; (3) Braunschweig University of Technology, Germany

While plants produce ROS for stress signaling and pathogen defense, they need to remove excessive ROS induced during stress responses in order to minimize oxidative damage. How can plants fine-tune the balance and meet such conflicting needs? Here, we show that xanthine dehydrogenase 1 (XDH1) in Arabidopsis appears to play spatially opposite roles to serve this purpose. Through a large-scale genetic screen, we identified three missense mutations in XDH1 that impair XDH1’s enzymatic functions, and underscore compromised powdery mildew resistance mediated by RPW8 in epidermal cells and formation of xanthine-enriched autofluorescent objects in mesophyll cells. Further analyses reveal that in leaf epidermal cells, XDH1 likely functions as an oxidase, along with NADPH oxidases RbohD and RbohF, to generate H2O2 that is enriched in the fungal haustorial complex in the infected epidermal cells for constraining the haustorium, thereby contributing to RPW8-dependent and RPW8-independent powdery mildew resistance. By contrast in leaf mesophyll cells, XDH1 performs its xanthine dehydrogenase activity to produce uric acid in local and systemic tissues to scavenge H2O2 from stress-impacted chloroplasts, thereby protecting plants from stress-induced oxidative damage. Thus, XDH1 plays spatially specified dual and opposing roles in modulation of ROS metabolism during defense response in Arabidopsis.

Abstract Number: P18-684
Session Type: Poster