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

Abstract

Lipopolysaccharides (LPS) are cell-surface components of Gramnegative 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 laserscanning 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.

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

“…General elicitors include flagellin, elongation factor Tu (EFTu), cold shock protein (CSP), chitin and LPS [123][124][125] . These compounds are conserved across multiple groups of bacteria, allowing plants to perceive and respond to an epitope that is common to many bacteria [123][124][125] . Plants respond to general elicitors with basal defence responses that can impart a measure of resistance to infection 52 .…”

“…One possible explanation is that antimicrobials produced in the LPS-treated leaf tissue prevent the bacteria from proliferating enough to activate a hypersensitive response 141 . By contrast, plant cells in culture often respond to LPS fractions from bacteria with an oxidative burst and transcription of defence genes 125 . For example, S. meliloti LPS core oligosaccharide can induce an oxidative burst in cultured cells of the non-host plant tobacco (Nicotiana tabacum) 128 .…”

The exudate from an arbuscular mycorrhizal fungus induces nitric oxide accumulation in Medicago truncatula roots

“…As a further control, we also tested bacterial LPS preparations, which are general elicitor of plant defense responses known to induce a rapid NO burst in plant systems (Zeidler et al 2004). LPS-induced NO accumulation could indeed be visualized in M. truncatula roots (Fig.…”

“…NO is well known to participate in plantpathogen interactions where it is rapidly produced during incompatible interactions with biotrophic pathogens as well as compatible interactions with necrotrophic pathogens (Delledonne et al 1998;Van Baarlen et al 2004). NO production is also induced by basal elicitors of plant responses such as bacterial lipopolysaccharides (LPS) (Zeidler et al 2004). Finally, evidence of NO involvement in plant symbioses is emerging; the use of NO-specific fluorescent probes has shown the occurrence of NO accumulation in the early (Shimoda et al 2005;Nagata et al 2008;del Giudice et al 2011) and late stages of the nitrogen-fixing symbiosis (NFS) that legumes establish with rhizobia (Baudouin et al 2006;Pii et al 2007;Horchani et al 2011).…”

Nitric oxide production and its functional link with OIPK in tobacco defense response elicited by chitooligosaccharide

“…4 The expression of defense-related enzymes in transcript levels by semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR). Treatment with SNP, P-Lys, cPTIO and L-NAME, NaN 3 and Tu on COS induced increases in the expression of CAT1 and PAL gene in wild-type and transgenic tobacco leaves at 3 h. Experiments were repeated three times in each treatment and obtained the same results Plant Cell Rep (2011Rep ( ) 30:1153Rep ( -1162Rep ( 1159 identified in plant, NOS-like activities have been detected in several types of plant species (Corpas et al 2006;Tian et al 2007) and mammalian NOS inhibitors could successfully suppress NO synthesis in plants and cell suspensions exposed to distinct elicitors (Delledonne et al 1998;Zeidler et al 2004;Mur et al 2005;Ali et al 2007), supporting that plant NOSlike enzyme may exist. NR is another enzyme which catalyzes the production of NO through an one-electron reduction of nitrite via the use of NAD(P)H as an electron donor in vitro assays.…”