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Table 2.7
CBEL elicitor induces defense genes through different SA, JA, and ET signaling
CBEL elicitor-induced expression of defense genes in wild-type
and mutant
Arabidopsis
plants
SA-defi cient
mutant
JA-defi cient
mutant
ET-defi cient
mutant
Plant defense genes
Wild-type
ASA1
(anthranilate
synthase)
+
+
−
+
PR-1
+
−
+
+
PDF1.2
(defensin)
+
+
−
−
Adapted from Khatib et al. (
2004
)
+, expressed; −, not expressed
while
E. carotovora
-derived polygalacturonase (PehA) elicitor induced only the JA/
ET signaling system in
Arabidopsis
(Kariola et al.
2003
). The HAMPs AtPep1 and
AtPep2 induced both JA/ET and SA signaling pathways in
A
.
thaliana
. These
HAMPs triggered expression of
PR-1
(the gene induced by SA) and
PDF1.2
(the gene induced by JA/ET) genes in
Arabidopsis
(Huffaker and Ryan
2007
).
In contrast, ZmPep1, the ortholog of AtPep1, activated de novo synthesis of JA and
ethylene, and not SA in maize (Huffaker et al.
2011
). A
-1,3-glucan sulfate elicitor
induced JA signaling system in grapevine (Trouvelot et al.
2008
).
The PAMP NLP
Pp
from
Phytophthora parasitica
strongly induced ethylene
biosynthesis enzymes ACC synthase (ACS) and ACC oxidase (ACO). However,
none of the genes encoding JA biosynthetic enzymes, such as lipoxygenase,
allene oxide synthase, allene oxide cyclase, 12-oxophytodienoate reductase, and
jasmonate-O - methyl transferase were altered in potato plants (Qutob et al.
2006
).
By contrast, rapid accumulation of transcripts encoding SA biosynthetic enzymes
such as isochorismate synthase 1 and phenylalanine ammonia-lyase was observed
(Qutob et al.
2006
). Collectively these studies indicate that NLP
Pp
may activate ET
and SA signaling pathways, but JA signaling pathway may not be involved in
NLPpp-mediated signaling system.
The PAMP CBEL induced different types of defense responses regulated by dif-
ferent signaling pathways (Table
2.7
; Khatib et al.
2004
). It induced the genes
PR-1
and
PDF1.2
encoding PR-1 and PR-12 defensin proteins, respectively and
ASA1
encoding anthranilate synthase involved in the biosynthesis of the phytoalexin
camalexin in
Arabidopsis
. Different signaling pathways were involved in the induc-
tion of these defense genes. The induction of
PR-1
was abolished in
NahG
plants,
which are defi cient in SA signaling, while the induction of
PDF1.2
and
ASA1
genes
was not altered in NahG plants. The results suggest that expression of PR-1 gene is
dependent of SA signaling system, but the expression of
PDF1.2
and
ASA1
is inde-
pendent of SA system. The CBEL-induced expression of
PDF1.2
was totally abol-
ished in
coi1
(JA-defi cient) and
ein2
(ET-defi cient) mutants and the PAMP-induced
expression of
ASA1
was abolished in
coi1
mutants. These results suggest that
expression of
PDF1.2
is dependent on the PAMP-induced JA/ET signaling systems,
β
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