Nitric oxide and salicylic acid signaling in plant defense.
Salicylic acid (SA) plays a critical signaling role in the activation of plant defense responses after pathogen attack. We have identified several potential components of the SA signaling pathway, including (i) the H(2)O(2)-scavenging enzymes catalase and ascorbate peroxidase, (ii) a high affinity SA-binding protein (SABP2), (iii) a SA-inducible protein kinase (SIPK), (iv) NPR1, an ankyrin repeat-containing protein that exhibits limited homology to IkappaBalpha and is required for SA signaling, and (v) members of the TGA/OBF family of bZIP transcription factors. These bZIP factors physically interact with NPR1 and bind the SA-responsive element in promoters of several defense genes, such as the pathogenesis-related 1 gene (PR-1). Recent studies have demonstrated that nitric oxide (NO) is another signal that activates defense responses after pathogen attack. NO has been shown to play a critical role in the activation of innate immune and inflammatory responses in animals. Increases in NO synthase (NOS)-like activity occurred in resistant but not susceptible tobacco after infection with tobacco mosaic virus. Here we demonstrate that this increase in activity participates in PR-1 gene induction. Two signaling molecules, cGMP and cyclic ADP ribose (cADPR), which function downstream of NO in animals, also appear to mediate plant defense gene activation (e.g., PR-1). Additionally, NO may activate PR-1 expression via an NO-dependent, cADPR-independent pathway. Several targets of NO in animals, including guanylate cyclase, aconitase, and mitogen-activated protein kinases (e.g., SIPK), are also modulated by NO in plants. Thus, at least portions of NO signaling pathways appear to be shared between plants and animals.
Waksman Institute and Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, 190 Frelinghuysen Road, Piscataway, NJ 08854-8020, USA. klessig@mcbl.rutgers.edu
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Klessig
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Durner
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Noad
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Navarre
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Wendehenne
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Kumar
J M
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Zhou
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Shah
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Zhang
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Kachroo
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Trifa
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Pontier
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Lam
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Silva
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D010947:Plants, Toxic; D020156:Salicylic Acid / Q000378:metabolism*; D015290:Second Messenger Systems; D015398:Signal Transduction; D014026:Nicotiana / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
D000246:Adenosine Diphosphate Ribose; D009569:Nitric Oxide; D020156:Salicylic Acid