A role for a flavin‐containing mono‐oxygenase in resistance against microbial pathogens in Arabidopsis

Abstract

SummaryUsing activation tagging in the Arabidopsis Col-0 rps2-101C background, we identified a mutant (FMO1-3D) that showed virtually no symptoms after inoculation with virulent Pseudomonas syringae pv. tomato DC3000 bacteria. The dominant, gain-of-function phenotype of the FMO1-3D mutant is due to over-expression of a class 3 flavin-containing mono-oxygenase (FMO). We recapitulated the FMO1-3D mutant phenotype in independent transgenic Col-0 lines over-expressing the FMO1 cDNA under the control of the 35S CaMV promoter. The increased basal resistance observed in the FMO1-3D mutant was also effective against the taxonomically unrelated downy mildew-causing pathogen Hyaloperonospora parasitica. By investigating the progeny from crosses of the FMO1-3D mutant with the NahG transgenic line, we showed that the enhanced basal resistance phenotype was dependent on the accumulation of salicylic acid. FMO1-3D plants showed wild-type resistant reactions after inoculation with avirulent bacteria, indicating that the R-gene-mediated defence physiology was not compromised by FMO1 over-expression. Transcripts of the class 3 FMO1 gene accumulated within 6 h after inoculation of wild-type Col-0 plants with avirulent Pst þ avrRpt2 cells. Moreover, a T-DNA insertion into the FMO1 gene resulted in enhanced susceptibility to virulent Pseudomonas and Hyaloperonospora parasitica, suggesting that expression of the FMO1 gene is a hitherto undescribed component of the plant's resistance repertoire. We discuss the possibility that the FMO may participate in the detoxification of virulence factors produced by pathogens.

Pipecolic Acid Orchestrates Plant Systemic Acquired Resistance and Defense Priming via Salicylic Acid-Dependent and -Independent Pathways

“…A largely Pip/FMO1-independent activation of the SA defense pathway at pathogen inoculation sites might explain why defects in Pip biosynthesis and FMO1 result in comparatively moderate decreases of basal immunity. In fact, the importance of FMO1 for local plant immune responses is variable and depends on the nature of the attacking pathogen, with particular significance of FMO1 for local immunity to pathogens that activate EDS1-dependent and SA-independent branches of plant defense (Bartsch et al, 2006;Koch et al, 2006). Interestingly, EDS1 and its interacting partner PAD4, both master regulators of basal immunity (Feys et al, 2001), have also been identified as necessary SAR components (Mishina and Zeier, 2006;Jing et al, 2011;Rietz et al, 2011;Breitenbach et al, 2014).…”

“…The strongly pathogen-inducible FMO1 gene encodes a flavin monooxygenase that is activated in both locally inoculated and distal leaves (Bartsch et al, 2006;Koch et al, 2006;Mishina and Zeier, 2006). Notably, functional FMO1 is necessary for SA accumulation in the systemic, noninoculated leaves but dispensable for SA production in inoculated tissue (Mishina and Zeier, 2006).…”

Light Regulation and Daytime Dependency of Inducible Plant Defenses in Arabidopsis: Phytochrome Signaling Controls Systemic Acquired Resistance Rather Than Local Defense

“…Our data also show that intact phytochrome signaling is required for pathogen-induced expression of FMO1 in noninoculated leaves. FMO1 is required for SAR in Arabidopsis, its overexpression confers increased plant resistance, and mutant plants unable to express the gene in distant tissue after a local infection, including phyAphyB, are all SAR deficient (Bartsch et al, 2006;Koch et al, 2006;Mishina and Zeier, 2006). During the SAR process, long-distance signal(s) generated in inoculated leaves are thought to travel through the plant and trigger resistance in distant tissue (Grant and Lamb, 2006;Park et al, 2007).…”

Bacterial flavin-containing monooxygenase is trimethylamine monooxygenase

“…FMOs have also been found in plants and fungi. Plant FMOs are involved in the biosynthesis of the plant-growth hormone auxin (6, 7) and in pathogen defense (8)(9)(10). In fungi, FMOs are vital for the functional expression of proteins that contain disulfide bonds by controlling the redox potential within the endoplasmic reticulum (11)(12)(13).…”