Innate immunity in Arabidopsis thaliana : Lipopolysaccharides activate nitric oxide synthase (NOS) and induce defense genes

doi:10.1073/pnas.0404536101

Innate immunity in Arabidopsis thaliana: Lipopolysaccharides activate nitric oxide synthase (NOS) and induce defense genes

Institutes of ^*Biochemical Plant Pathology, ^¶Radiobiology, and ^∥Pathology, GSF-National Research Center for Environment and Health, D-85764 Neuherberg, Germany; ^§Biochemical Pharmacology, University of Konstanz, D-78464 Konstanz, Germany; ^‡Department of Biochemistry, Rand Afrikaans University, Auckland Park 2006, Johannesburg, South Africa; and ^†Division of Immunochemistry, Research Center Borstel, D-23845 Borstel, Germany

Edited by Frederick M. Ausubel, Harvard Medical School, Boston, MA (received for review June 24, 2004)

Abstract

Lipopolysaccharides (LPS) are cell-surface components of Gram-negative bacteria and are microbe-/pathogen-associated molecular patterns in animal pathosystems. As for plants, the molecular mechanisms of signal transduction in response to LPS are not known. Here, we show that Arabidopsis thaliana reacts to LPS with a rapid burst of NO, a hallmark of innate immunity in animals. Fifteen LPS preparations (among them Burkholderia cepacia, Pseudomonas aeruginosa, and Erwinia carotovora) as well as lipoteichoic acid from Gram-positive Staphylococcus aureus were found to trigger NO production in suspension-cultured Arabidopsis cells as well as in leaves. NO was detected by confocal laser-scanning microscopy in conjunction with the fluorophore 4-amino-5-methylamino-2′,7′-difluorofluorescein diacetate, by electron paramagnetic resonance, and by a NO synthase (NOS) assay. The source of NO was addressed by using T-DNA insertion lines. Interestingly, LPS did not activate the pathogen-inducible varP NOS, but AtNOS1, a distinct NOS previously associated with hormonal signaling in plants. A prominent feature of LPS treatment was activation of defense genes, which proved to be mediated by NO. Northern analyses and transcription profiling by using DNA microarrays revealed induction of defense-associated genes both locally and systemically. Finally, AtNOS1 mutants showed dramatic susceptibility to the pathogen Pseudomonas syringae pv. tomato DC3000. In sum, perception of LPS and induction of NOS contribute toward the activation of plant defense responses.

Footnotes

↵ ** To whom correspondence should be addressed. E-mail: durner{at}gsf.de.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: DA, diacetate; DAF-FM, 4-amino-5-methylamino-2′,7′-difluorofluorescein; LPS, lipopolysaccharides; LTA, lipoteichoic acid; NOS, NO synthase; iNOS, pathogen-inducible NOS; NR, nitrate reductase; PAMP, pathogen-associated molecular patterns; PR, pathogenesis related; TLR, Toll-like receptor.