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whereas the expression of
ASA1
is dependent on JA signaling system in
Arabidopsis
(Khatib et al.
2004
). Collectively, these results suggest that the PAMP CBEL activates
different hormone signaling systems and triggers various defense responses.
2.27.2
Some PAMPs May Activate Multiple Hormone
Signaling Systems
Some PAMPs may not have any specifi city in activating different hormone signaling
systems. The PAMP NPP1 from
Phytophthora sojae
triggers ethylene production
and also SA signaling pathway (Fellbrich et al.
2002
). Pep-13, a PAMP from
Phytophthora
, induces the accumulation of both SA and JA and also activates defense
genes in potato (Halim et al.
2009
). The PAMP fl g22 induces both SA-dependent
PR-1
expression and JA/ET-dependent
PDF1.2
expression in
Arabidopsis
(Gómez-
Gómez et al.
1999
). Flg22 activates SA, JA and ET signaling pathways and OGs
also activate these three pathways (Denoux et al.
2008
). These studies demonstrate
that different PAMPs may activate various signaling systems and some of them may
be specifi c in activating specifi c signaling systems.
2.28
PAMPs May Function Differently in Different Plants
The PAMPs may behave differently in different plant system. They may trigger
variable downstream signaling responses in different plants. Khatib et al. (
2004
)
observed enhanced
-1,3-glucanase activities after infi ltration of CBEL in leaves
belonging to four different botanical families, i.e. tobacco (Solanaceae),
Arabidopsis
(Brassicaceae), French bean (Fabaceae) and
Zinnia
(Asteraceae). However, other
species of the same families such as pea and sunfl ower did not respond to CBEL
(Khatib et al.
2004
).
The harpin (HrpN
ea
) from
Erwinia amylovora
induces increases in anion current in
apple cells, while it decreases the anion current in
Arabidopsis
cells (Reboutier et al.
2007
). In apple cells, harpin did not trigger any signifi cant H
2
O
2
production, while in
Arabidopsis
cells, a rapid transitory increase of H
2
O
2
production was observed within
30 min of the elicitor treatment (Reboutier et al.
2007
). These results suggest that the
PAMPs may trigger defense responses depending on the specifi c host plants.
β
2.29
Specifi city of PAMPs in Triggering Immune
Responses in Plants
The PAMPs may trigger immune responses in some specifi c plants. The bacterial
PAMP CSP22 triggers defense responses specifi cally in Solanaceous plants (Felix
and Boller
2003
). The bacterial PAMP EF-Tu triggers immune responses only in
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