Table 1.

Elicitors found in the apoplastic space.

Elicitor	Source	Receptor	Receptor type	Reference
Exogenous
csp22	Bacterial cold shock protein	Unknown		Felix and Boller (2003)
elf18	Bacterial Elongation Factor Tu (EF-Tu)	EFR	LRR	Kunze et al. (2004), Zipfel et al. (2006)
flg22	Bacterial flagellin	FLS2	LRR	Felix et al. (1999), Gómez-Gómez et al. (1999)
				Gómez-Gómez and Boller (2000)
				Chinchilla et al. (2006)
Pep13	Oomycete transglutaminase	Unknown		Brunner et al. (2002)
CBD2synt	Oomycete cellulose-binding elicitor lectin (CBEL)	Unknown		Gaulin et al. (2006)
Peptidoglycan (PGN)	Bacterial cell wall (Gram positive)	Lym1, Lym3	LysM	Gust et al. (2007), Willmann et al. (2011)
Lipopolysaccharide (LPS)	Bacterial cell wall (Gram negative)	Unknown		Newman et al. (1995)
Chitin fragments	Fungal cell wall	CeBip, CERK1, AtCERK1	LysM	Felix et al. (1993), Kaku et al. (2006)
				Miya et al. (2007)
				Shimizu et al. (2010)
Beta Glucan (GE)	Oomycete cell wall	Beta Glucan Binding Protein (GBP)	Glycosyl hydrolase family	Albersheim and Valent (1978) Umemoto et al. (1997),
				Fliegmann et al. (2004)
Xylanase (EIX)	Fungal xylanase	EIX1/2	LRR	Bailey et al. (1990), Ron and Avni (2004)
				Bar et al. (2010)
Endogenous
Cutin monomers	Plant cell wall	Unknown		Schweizer et al. (1996)
				Fauth et al. (1998)
Hydroxyproline-rich Systemin glycopeptides (HypSys)	Cytosolic plant protein	Unknown		Pearce et al. (2001)
Oligogalacturonides (OGs)	Plant cell wall	WAK1	EGF-like	Hahn et al. (1981), Brutus et al. (2010)
				Nothnagel et al. (1983)
AtPeps	Cytosolic plant protein	PEPR1/PEPR2	LRR	Huffaker et al. (2006), Yamaguchi et al. (2006)
				Yamaguchi et al. (2010)
Systemin	Cytosolic plant protein	Unknown		Pearce et al. (1991)