PAMP Signaling in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 91

2.20.9 Jasmonate Signaling System

PAMPs have been shown to trigger accumulation of jasmonic acid (Wang et al.
2000; Fabro et al. 2008 ). The fungal PAMP chitosan treatment induced accumulation
of jasmonic acid in tomato leaves (Doares et al. 1995 ). Several enzymes including
lipoxygenase, allene oxide synthase, allene oxide cyclase, OPDA reductase 3
(OPR3) and acyl-CoA oxidase (ACX) are involved in biosynthesis of jasmonic acid
(JA) (Mei et al. 2006 ; Schilmiller et al. 2006; Balbi and Devoto 2008 ; Delker et al.
2007 ; Vidhyasekaran 2007a ). Flg22 induced the activation of JA signaling system.
It enhanced the expression of LOX3 and LOX4 genes encoding lipoxygenases
(LOX), OPR3 gene encoding 12-oxophytodienoate reductase (OPR) and ACX1
gene encoding acyl-CoA oxidase (ACX) (Denoux et al. 2008 ). The fungal PAMP
chitosan also activates lipoxygenase, the key enzyme in JA-mediated signaling sys-
tem (Bohland et al. 1997 ; Rakwal et al. 2002). Lipoxygenase activity signifi cantly
increased in chitosan-treated carrot plants (Jayaraj et al. 2009). The PAMP

-1,3-
glucan induces expression of LOX gene encoding lipoxygenase in grapevine (Aziz
et al. 2003 ; Balbi and Devoto 2008 ) and tobacco cells (Klarzynski et al. 2000 ). The
PAMP Nep1 rapidly induces genes involved in JA biosynthesis (Bae et al. 2006 ). It
triggered genes encoding lipoxygenases ( LOX ), 12-oxophytodienoate reductase,
and allene oxide cyclase ( AOC2 ), which are involved in JA biosynthesis (Bae et al.
2006 ). The HAMP oligogalacturonates triggered OPR3 and ACX1, the key enzymes
involved in biosynthesis of JA (Denoux et al. 2008 ).
JA can be metabolized to several derivatives and some of them are involved in
defense signaling system. Methyl jasmonate is one of these JA derivatives, which
trigger the immune signaling system (Seo et al. 2001 ). JA is converted to methyl
jasmonate (MeJA) by the action of jasmonic acid methyl transferase (Wasternack
2007). The JA amino acid conjugate JA-Ile (jasmonoyl-isoleucine) also has been
shown to be involved in defense signaling (Kang et al. 2006 ; Katsir et al. 2008 ).
JA-amino synthetase activates conjugation of JA to an amino acid and this enzyme
may be involved in JA-Ile biosynthesis (Staswick and Tiryaki 2004). In addition to
Ile, the JAR family of related GH3 enzymes has the potential to conjugate other
amino acids, such as Trp, Val, and Leu in tobacco. The JA-Trp, JA-Val, and JA-Leu
may also participate in JA signaling pathway (Wang et al. 2008c ).
G-proteins activated Ca 2+ infl ux and the subsequent Ca 2+ wave may initiate calmod-
ulin-dependent protein kinase cascade, ROS production, and eventually the jasmonate
biosynthesis (Zhao et al. 2004; Trusov et al. 2006). MAPK cascades may also be
involved in JA biosynthesis (Lee et al. 2004; Kandoth et al. 2007). NO is involved
in induction of biosynthesis of JA (Xu et al. 2005; Palmieri et al. 2008). NO induces
the key enzymes of the JA biosynthesis pathway (del Rio et al. 2004; Grün et al.
2006; Zago et al. 2006 ). Several PAMPs are known to activate plant innate immu-
nity by triggering the action of several components in the JA signaling system. The
oomycete PAMP cryptogein induced an increase in lipoxygenase activity and the
accumulation of JA-responsive proteinase inhibitors in tobacco suggesting the role of
JA signaling system in the PAMP-mediated disease resistance (Bottin et al. 1994).

β