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.
Klessig
D F
DF
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
Durner
J
J
Noad
R
R
Navarre
D A
DA
Wendehenne
D
D
Kumar
D
D
Zhou
J M
JM
Shah
J
J
Zhang
S
S
Kachroo
P
P
Trifa
Y
Y
Pontier
D
D
Lam
E
E
Silva
H
H
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