Reactive Oxygen Species and Cognate Redox Signaling System in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 292

(Kwak et al. 2003 ; Wang et al. 2006 ). Calcium-permeable channels are activated by
ROS and ABA signaling network is involved in the ROS-induced activation of cal-
cium-permeable channels (Pei et al. 2000 ; Murata et al. 2001 ; Trouverie et al. 2008 ;
Zhang et al. 2011 ). Activation of these channels requires the presence of NAD(P)H
in the cytosol. Type 2C protein phosphatases (PP2Cs) also play a role in the ABA-
induced ROS-dependent activation of calcium channels (Murata et al. 2001 ). Anion
channel activation and proton pumping inhibition involved in the plasma membrane
depolarization induced by ABA in A. thaliana suspension cells were shown to be
ROS dependent (Trouverie et al. 2008 ). H 2 O 2 mediates, at least in part, ABA
responses including stomatal closure and gene expression (Guan et al. 2000 ; Pei
et al. 2000 ).

5.14 ROS Activates Phosphorylation/Dephosphorylation

Systems

Protein phosphorylation plays a central role in plant immune response signaling
(Peck et al. 2001 ; Nürnberger et al. 2004 ; Zipfel et al. 2004 ; Benschop et al. 2007 ;
Tena et al. 2011 ). Protein kinases and protein phosphatases and their corresponding
protein substrates play key roles in signal transduction. The proteins that make up the
signal transduction pathway are present in the cell prior to the perception of elicitor
(Benschop et al. 2007 ). These proteins are activated by post-translational modifi ca-
tions and conformational changes. The most widely recognized post-translational
modifi cation involved in signal transduction is protein phosphorylation (Benschop
et al. 2007 ). Post-translational protein modifi cation by phosphorylation/dephosphor-
ylation is an important component in defense signaling system (Lecourieux-Ouaked
et al. 2000 ; Peck et al. 2001 ; Romeis et al. 2001 ; Lecourieux et al. 2002 , 2006 ).
ROS plays important role in triggering phosphorylation of proteins involved in
defense signaling system. The genes encoding serine/threonine/tyrosine kinases
involved in protein phosphorylation are induced by H 2 O 2 in Arabidopsis (Desikan
et al. 2001 ) and Nicotiana tabacum (Vranová et al. 2002 ; Vandenabeele et al. 2003 ).
Calcium-dependent protein kinase is induced by ROS in Arabidopsis (Desikan et al.
2001 ). Phosphorylation induced by MAP kinases has been shown to be involved in
ROS signaling (Ren et al. 2002 ; Yoshioka et al. 2003 ; Nakagami et al. 2006 ; Zhang
et al. 2006 ; Xing et al. 2007 , 2008 ). MAP kinase cascades have been shown to be
involved in phosphorylation of transcription factors (Asai et al. 2002 ; Nakagami
et al. 2006 ). Another kinase involved in H 2 O 2 signaling is oxidative signal-inducible
1 (OXI1) (Rentel et al. 2004 ). One of the genes activated by H 2 O 2 in Arabidopsis is
that encoding a protein Tyr phosphatase (Desikan et al. 2001 ). Protein Tyr phospha-
tases are important signaling enzymes that regulate protein phosphorylation events
(Fauman and Saper 1996 ). The Arabidopsis protein phosphatase 2C enzymes ABI1
and ABI2 and the protein tyrosine phosphatase AtPTP1 are inactivated by ROS
(Meinhard and Grill 2001 ; Gupta and Luan 2003 ). These studies suggest that ROS
is involved in modulating the phosphorylation process in innate immune responses.