Nitric Oxide Signaling System in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 319

GSNO affects PrxII E activity through S-nitrosylation of the Cys residues. GSNO
has been shown to be able to S-nitrosylate PrxII E in vivo ((Romero-Puertas et al.
2007 ). ONOO − is an important signal molecule involved in triggering accumulation
of PR proteins (Durner et al. 1998 ).

6.9 Role of NO in Protein Nitration

NO can also perform posttranslational protein modifi cations through nitration,
besides through S-nitrosylation (Zaninotto et al. 2006 ). Peroxynitrite (ONOO − ), the
reactive nitrogen species is generated by the reaction of NO with superoxide anion
(O 2 - ) (Bryk et al. 2000 ; Neill et al. 2008 ; Vandelle and Delledonne 2011 ). During
the hypersensitive reaction (HR), the formation of ONOO − is promoted by the rate
of NO reaction with O 2 − , which is approximately three times faster than the reaction
of O 2 − with superoxide dismutase (SOD) forming H 2 O 2 during the oxidative burst
(Ichiropoulos and al-Mehdi 1995 ). ONOO − generation in tobacco cells treated with
an oomycete elicitor occurred within 1 h and reached a maximum level at 6-12 h
after elicitor treatment (Saito et al. 2006 ). Urate, a ONOO − scavenger, abolished
elicitor-induced ONOO − generation (Saito et al. 2006 ).
ONOO − causes protein tyrosine nitration through the nitration of Tyr residues in
Tyr kinase (Schopfer et al. 2002 ; Radi 2004 ; Romero-Puertas et al. 2008 ). ONOO − donor
SIN-1 [3-(4-morpholinyl) sydnonimine hydrochloride) treatment induced nitrotyro-
sine-containing proteins in tobacco cells (Saito et al. 2006 ). The number of nitrated
proteins increased during disease resistance response in Arabidopsis thaliana
(Romero-Puertas et al. 2008 ). Protein extracts from leaves of A. thaliana treated with
ONOO − showed a signifi cant increase in nitrated proteins when pretreated with GSNO
(Romero-Puertas et al. 2008 ). ONOO − was found to induce protein nitration in
soybean and tobacco (Delledonne et al. 2001 ; Saito et al. 2006 ).
S -nitrosylation inhibits the ONOO − detoxifi cation activity of peroxiredoxin II E
(PrxII E), causing a dramatic increase of ONOO − -dependent nitrotyrosine residue
formation. The same increase was observed in prxII E mutant line after exposure to
ONOO − , indicating that PrxII E modulation of ONOO − is important in the signaling
system (Romero-Puertas et al. 2008 ). ONOO − may have important signaling func-
tions in plants. SIN, an NO donor that provides continuous source of ONOO − was
found to induce the accumulation of the transcript encoding PR-1 in tobacco leaves
(Durner et al. 1998 ).
Protein nitration alters catalytic activity and interferes with cellular signaling pro-
cesses (Schopfer et al. 2002 ). Protein nitration is a reversible and selective process
associated with protein Tyr phosphorylation (Klotz et al. 2002 ). Tyr phosphorylation
may mediate signaling events induced by nitrating agents like ONOO − and depending
on ONOO − local concentrations, the nitration and phosphorylation of critical Tyr resi-
dues may be competing processes (Brito et al. 1999 ). Several protein phosphatases
have been characterized in plants, implying that Tyr phosphorylation and dephos-
phorylation also serve important functions in signaling system (Luan 2002 ).