PAMP Signaling in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 101

Table 2.6 Synergistic action of PAMPs/elicitors in induction of different PR genes in Arabidopsis

HrpN PehA HrpN + PehA

PR gene 24 h 48 h 24 h 48 h 24 h 48 h

PR1 + ++ − − ++ +++

PDF 1.2 − − − ++ +++ +++

Adapted from Kariola et al. ( 2003 )
−, not detected; +, ++, +++, increased intensity of expression of defense genes

2.24.2 Different PAMPs May Act Synergistically

The different PAMPs may act synergistically in inducing expression of defense
response. N-acetylchitoheptaose and tetraglucosyl glucitol are the two oligosaccharide
PAMPs derived from the rice blast pathogen Magnaporthe grisea cell walls. The
two PAMPs were recognized by different receptors. However, they synergistically
activated phytoalexin biosynthesis in cultured rice cells, suggesting that different
PAMPs may act synergistically in inducing expression of defense response
(Yamaguchi et al. 2002 ). There was a signifi cant enhancement of PAMP-induced
calcium ion infl ux when the following PAMPs were combined, compared with the
effect of the individual PAMPs: fl g22 + elf18; fl g22 + LOS; fl g22 + core oligosac-
charides; and LOS + core oligosaccharides. These increases were additive, except
for fl g22 and LOS, where there appears to be synergy (Aslam et al. 2009 ).
Harpin (HrpN) and polygalacturonase (PehA) are the two Erwinia carotovora
subsp. carotovora -derived elicitors. Both of them individually did not induce signifi -
cant amount of production of superoxide in Arabidopsis . In contrast, they triggered
increased production of superoxide when the two elicitors were applied simultane-
ously (Kariola et al. 2003 ). The harpin elicitor induced both SA and JA/ET signaling
pathways, as indicated by induction of the SA-signaling system marker gene PR-1
and the JA/ET-signaling system marker gene PDF1.2. PehA elicitor induced only JA/
ET signaling system. However, when both the elicitors were applied simultaneously,
they triggered faster and higher expression of both the SA and JA/ET signaling sys-
tems (Table 2.6 ; Kariola et al. 2003 ). The results suggest that some PAMPs/elicitors
may act synergistically in induction of defense signaling systems. Some PAMPs have
additive effect and the fl agellin peptide (fl g22) and elongation factor 18 (elf18) show
additive effect in inducing defense signaling system (Aslam et al. 2009 ).

2.24.3 Some PAMPs May Show Antagonistic Effect

in Activating Defense Responses

Some PAMPs show antagonistic effect between them. The fl g22 and oligosaccharide
elicitor (OGA) showed mutual interference between them. OGA suppresses fl g22-
induced defences in Arabidopsis (Aslam et al. 2009 ). Reduced calcium infl ux was