PAMP Signaling in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 37

2.7.2 β -Glucan PAMPs Isolated from Fungal Cell Wall

Glucans are important components of cell walls of various fungi and oomycetes.
Several

-glucan poly- and oligosaccharides seem to be generated from fungal and
oomycete cell walls at the site of infection through the action of plant

β

β -1,3- glucanases

(Silipo et al. 2010 ). Most of these -glucan wall components have been recognized as

PAMPs (Yamaguchi et al. 2000a , b ; Klarzynski et al. 2000 ; Shibuya and Minami
2001 ; Silipo et al. 2010 ). These fragments may act differently in different plants. A
glucan fragment, tetraglucosyl glucitol from Magnaporthe oryzae is active in rice
cells, but not in soybean (Yamaguchi et al. 2000a , b ).

β

-1,3 glucan oligomers with a
degree of polymerization (DP) 4 and DP 6 trigger defense responses (Inui et al. 1997 ).

β

2.7.3 Fungal Cell Wall Ergosterol PAMP

Ergosterol is a typical fungal sterol, which is absent in plants. It has been detected
in cell walls of most fungi (Kasparovsky et al. 2003 , 2004; Laquitaine et al. 2006 ;
Lochman and Mikes 2006). Ergosterol is perceived by plant cells. It triggers pro-
duction of ROS even at nano-molar concentrations in tobacco and tomato cells. It
also activates mitogen-activated protein kinases on alfalfa cells (Lochman and
Mikes 2006). The ergosterol induced oxidative burst and it enhanced NADPH
oxidase and superoxide dismutase activities (Rossard et al. 2010 ). Based on these
elicitor activities and wide occurrence in fungal species, and its absence in plants,
ergosterol has been recognized as a PAMP (Naito et al. 2008 ).

2.7.4 EIX Protein as PAMP

The fungal protein ethylene-inducing xylanase (EIX) is a PAMP inducing defense
reactions in tobacco and tomato (Bailey et al. 1990 ; Avni et al. 1994 ). EIX is a
potent elicitor of plant defense responses in specifi c cultivars of tobacco and tomato
(Bar et al. 2010 ). EIX was shown to specifi cally bind to the plasma membrane of
both tomato and tobacco responsive cultivars (Hanania and Avni 1997 ). The
response to EIX in tobacco and tomato cultivars is controlled by a leucine-rich-
repeat receptor-like-protein (LRR-RLP) encoded by a single locus, termed LeEix
(Ron and Avni 2004 ).

2.7.5 Cerebrosides as PAMPs

Cerebrosides A, B. and C. categorized as sphingolipids are novel elicitors detected
in a wide range of pathogens (Koga et al. 1998; Umemura et al. 2000). Sphingolipid
is a structural component of many eukaryotic cell membranes and has been shown