PAMP Signaling in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 24

Table 2.1 PAMPs/pathogens induced expression of the HAMP/endogenous elicitor
PROPEP2 in Arabidopsis

Fold change in PROPEP2
gene expression PAMPs/pathogens

PAMP fl g22 21.8

PAMP HrpZ 40.8

PAMP NPP1 26.9

Fungal pathogen Botrytis cinerea 27.9

Oomycete pathogen Phytophthora infestans 31.2

Bacterial pathogen Pseudomonas syringae 3.2

Adapted from Huffaker et al. ( 2006 )

original PAMP signals and therefore they can also be called “PAMP amplifi ers”
(Huffaker and Ryan 2007 ).
Several PAMPs including Flg22, NPP1, and HrpZ and pathogens including Botrytis
cinerea , Phytophthora infestans , and Pseudomonas syringae trigger expression of
PROPEP2 gene encoding PROPEP2, the precursor for the endogenous elicitor AtPep2
(Table 2.1 ; Huffaker et al. 2006 ). Similar induced expression of genes encoding
PROPEP3 and PROPEP1 due to PAMP and pathogens treatment has also been reported
(Huffaker et al. 2006 ). Treatment with the bacterial PAMP fl g22 upregulates the tran-
scription of genes encoding PROPEP family precursors for the endogenous elicitors
AtPeps and PEPR receptors (Zipfel et al. 2004 ; Ryan et al. 2007 ). These endogenous
elicitors are also induced by fungal pathogen infection (Huffaker et al. 2011 ).
At Pep family elicitors and the classical PAMPs activate similar downstream
responses using many of the same molecular components (Ryan et al. 2007 ; Krol
et al. 2010 ; Postel et al. 2010 ; Qi et al. 2010 ; Yamaguchi et al. 2010 ; Huffaker et al.
2011 ). Both the PAMP fl g22 and the endogenous elicitors AtPeps bind specifi c
LRR receptors and both activate the same downstream signaling events (Yamaguchi
et al. 2006 ; Huffaker and Ryan 2007 ; Krol et al. 2010 ). The endogenous elicitor
AtPep1 treatment induces the transcription of FLS2, the PRR for the PAMP fl g22
(Ryan et al. 2007 ). The receptors for both fl g22 and AtPep1 associate with the inter-
acting receptor partner, BAK1 (Ma et al. 2009 ; Postel et al. 2010 ). Collectively
these studies suggest that the endogenous elicitors are functionally similar to classi-
cal PAMPs and may act as amplifi ers of PAMP-induced signals.

2.6 Bacterial PAMPs

2.6.1 PAMPs from Various Bacterial Structures

Several PAMPs have been isolated and characterized from wide range of bacterial
pathogens. These PAMPs have been purifi ed from bacterial fl agella structure and
bacterial cell envelope lipopolysaccharides and peptidoglycans. PAMPs have also