Nitric Oxide Signaling System in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 306

6.1 Nitric Oxide as a Component of the Repertoire of Signals

Involved in Plant Immune Signaling System

Nitric oxide (NO) is a gaseous readily diffusible free radical identifi ed as a signaling
molecule in animals and plants (Besson-Bard et al. 2008a , b ). Nitric oxide (NO) is a
key mediator for rapid induction of plant immune responses (Bellin et al. 2013 ). It is
now well-accepted that NO is a component of the repertoire of signals that a plant
uses to both thrive and survive (Wilson et al. 2008 ). On perception of pathogen asso-
ciated molecular patterns (PAMPs), plant pattern recognition receptors (PRRs) mod-
ulate signaling networks for defense responses that rely on rapid production of
reactive nitrogen species (RNS) and reactive oxygen species (ROS) (Bellin et al.
2013 ). NO is a diffusible molecular messenger that plays an important role in the
plant immune response signal transduction system (Grennan 2007 ). Involvement of
NO in defense signaling has been well demonstrated (Durner et al. 1998 ; Delledonne
et al. 2001 ; Polverari et al. 2003 ; Xu et al. 2004 ; Perchepied et al. 2010 ; Chun et al.
2012 ). NO biosynthetic genes NIA1 and NIA2 have been shown to induce NO syn-
thesis and defense responses in Arabidopsis . Expression of the defense-related genes
was either abolished or delayed in the double mutant. The double mutant nia1 nia2
plants were highly susceptible to Sclerotinia sclerotiorum (Perchepied et al. 2010 ).
The transgenic tobacco plants constitutively expressing a mammalian neuronal nitric
oxide synthase (NOS) involved in NO production exhibited enhanced resistance to a
spectrum of pathogens, including bacteria, fungi, and viruses (Chun et al. 2012 ).
Collectively these results demonstrate the role of NO in defense signaling.
An oomycete PAMP/elicitor triggers a NO burst within minutes in tobacco cells
(Foissner et al. 2000 ; Lamotte et al. 2004 ). A transient burst of NO has been observed
in roots of Arabidopsis thaliana as an early response after contact with Verticillium
longisporum (Tischner et al. 2010 ). NO acts substantially in cellular signal trans-
duction through stimulus-coupled S-nitrosylation of cysteine residues (Benhar et al.
2008 ). It serves as a key redox-active signal for the activation of various defense
responses (Klessig et al. 2000 ). NPR1 and TGA1 are key redox-controlled regula-
tors of systemic acquired resistance (SAR) in plants. The translocation of NPR1
into the nucleus has been shown to be promoted by NO, suggesting that NO is a
redox regulator of the NPR1/TGA1 system involved in SAR (Lindermayr et al.
2010 ). Collectively these studies suggest that NO plays an important role in plant
innate immunity signaling system.

6.2 PAMP-Induced Biosynthesis of NO in Plants

NO may be synthesized through different pathways (Fig. 6.1 ; Planchet et al. 2006 ;
Yamasaki and Cohen 2006 ; Zhao et al. 2007 ; Zottini et al. 2007 ). NO is synthesized
predominantly by the enzyme NOS in mammals (Bethke et al. 2004 ). NOS cataly-
ses NO production from the substrate arginine and requires Ca 2+ /CaM activation
(Crawford et al. 2006 ).