Reactive Oxygen Species and Cognate Redox Signaling System in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 284

PAMP SIGNAL

Ca 2+
influx

K - and
Cl -
effluxes

NO3
efflux

G-
proteins

Plasma
membrane
depolarization

MAP
kinases

CDPKs

Activation of NADPH oxidase

ROS generation

Fig. 5.2 PAMP-triggered early signaling events activating NADPH oxidase to produce ROS

5.2.2 Early PAMP-Induced Events Leading to Activation

of NADPH Oxidase to Generate ROS

The early PAMP elicitor-induced events include Ca 2+ infl ux, anion effl uxes,
cytosolic acidifi cation, plasma membrane depolarization, MAPK signaling
cascade activation, calcium-dependent protein kinase (CDPK) activation, and
protein phosphorylation/dephosphorylation. These events have been shown to
activate NADPH oxidase homologs of plants termed respiratory burst oxidase
homolog (Rboh) which is responsible for ROS production (Fig. 5.2 ; Nürnberger
and Scheel 2001 ; Simon-Plas et al. 2002 ; Wendehenne et al. 2002 ; Apel and Hirt
2004 ; Kadota et al. 2004 ; Torres and Dangl 2005 ; Wong et al. 2007 ; Asai et al.
2008 ; Zhu et al. 2009 ; Zhao et al. 2010 ; Zhang et al. 2011 ; Kiirika et al. 2012 ).
The NADPH oxidases are localized to plasma membrane fractions (Keller et al.
1998 ) and are stimulated directly by Ca 2+ (Sagi and Fluhr 2001 ). All plant rboh
genes carry EF-hands that bind Ca 2+ and plant Rboh proteins were shown to be
stimulated directly by Ca 2+ (Jabs et al. 1997 ; Sagi and Fluhr 2001 ; Torres and
Dangl 2005 ; Van Breusegem et al. 2008 ). NO 3 − effl ux activation seems to be
essential to induce NADPH oxidase (Wendehenne et al. 2002 ). Anion effl ux has
been shown to be necessary for the induction of ROS production in parsley (Jabs
et al. 1997 ) and soybean cells (Ebel et al. 1995 ). Phosphorylation events also
occur both upstream and downstream of ROS production (Nürnberger and Scheel
2001 ; Apel and Hirt 2004 ).