PAMP Signaling in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 86

Ori et al. 1997) have been shown to be involved in triggering ROS production.
Different PAMPs may induce ROS production by different types of enzymes (Allan
and Fluhr 1997). Cultured cells of rose treated with a PAMP derived from
Phytophthora spp. produced ROS by a NADPH oxidase, whereas the cultured cells
of French bean treated with a PAMP from Colletotrichum lindemuthianum produced
ROS by the action of a cell wall peroxidase (Bolwell et al.1995, 1998). The tran-
script encoding NADPH oxidase ( AtrbohD ) was up-regulated (7.2 fold) by the
PAMP Nep1 treatment and it generated ROS in Arabidopsis (Bae et al. 2006 ).
Flagellin treatment triggers the expression of RbohD and RbohC genes encoding
NADPH oxidases involved in generation of ROS (Denoux et al. 2008 ).
G-proteins regulate the production of ROS by activating the NADPH oxidase
(Joo et al. 2005 ; Moeder et al. 2005; Wong et al. 2007). MAP kinases may also be
involved in generation of ROS by activating the NADPH oxidase (Asai et al. 2008 ).
Calcium-dependent protein kinase (CDPK) has also been shown to phosphorylate
NADPH oxidase and trigger ROS production (Xing et al. 1997; Blumwald et al.
1998). Accumulation of ROS requires both Ca 2+ infl ux and protein kinase activity
(Bolwell et al. 1995; Romeis et al. 1999).
ROS plays a central role in launching the defense response (Vandenabeele
et al. 2003). It interacts with various defense signaling systems and activates Ca 2+
signaling system, NO signaling system, salicylic acid signaling system, jasmo-
nate signaling system and ethylene signaling system (León et al. 1995; Desikan
et al. 2001; Vranová et al. 2002; Vandenabeele et al. 2003; Fedoroff 2006;
Hancock et al. 2006; Torres et al. 2006 ). The functions of ROS in the signaling
network are described in Chap. 5 .

2.20.6 Nitric Oxide Signaling System

PAMPs are known to trigger nitric oxide (NO) burst within minutes in plant cells
(Foissner et al. 2000; Lamotte et al. 2004 ). The bacterial PAMP harpin induces NO
generation in Arabidopsis cells (Krause and Durner 2004). The bacterial PAMP
lipopolysaccharide (Lipid A) generates a rapid burst of NO production in Arabidopsis
cells (Zeidler et al. 2004 ). Treatment of tomato cell cultures with the fungal PAMP
xylanase resulted in a rapid NO accumulation (Laxalt et al. 2007).
NO is a gaseous readily diffusible free radical which acts as a messenger in plant
immune signaling system (Besson-Bard et al. 2008; Wilson et al. 2008 ). NO may be
synthesized through different pathways (Planchet et al. 2006; Yamasaki and Cohen
2006; Zhao et al. 2007; Zottini et al. 2007). NO is synthesized predominantly by
nitric oxide synthase (NOS) (Zhao et al. 2007; Zottini et al. 2007). The PAMP fl g22
triggered the expression of AtNOS1 encoding nitric oxide synthase (NOS) (Denoux
et al. 2008 ). NOS catalyses nitric oxide (NO) production (Crawford et al. 2006), sug-
gesting that the PAMP activates NO signaling system. Polyamines may also be
involved in NO synthesis (Tun et al. 2006; Besson-Bard et al. 2008) and polyamine
oxidases or some unknown enzymes may be involved in the generation of NO from