Disease cycle of potato late blight - MSpace at the University of ...

Defense suppressors may:
1) Inhibit the interactions between the elicitor from the pathogen and the corresponding
receptor from the plant by blocking the receptor site;
2) Block the signal transduction pathway during the elicitor-mediated activation of the
defense response;
3) Affect the formation of binding complexes in the promoter region and suppress the
expression of specific genes (Shiraishi et al. 1994).
For example, saponin-degrading enzymes have been isolated from a number of
plant pathogenic fungi. Gaeumannomyces graminis var. avena produces the degrading
enzyme avenacinase that detoxifies the phytoanticipin avenacin (Bowyer et al. 1995) and
Septoria lycopersici produces the degrading enzyme tomatinase that detoxifies the
phytoanticipin tomatine (Bouarab et al. 2002). A recent report by Rose et al. (2002)
provided the first molecular evidence that fungi may suppress antifungal proteins. A class
of glucanase inhibitor proteins (collectively called GIPs) has been characterized in the
soybean oomycete pathogen Phytophthora sojae (Rose et al. 2002). Also, pathogens can
inactivate reactive oxygen species (ROS) with peroxidases, catalases and superoxide
dismutase (Mayer et al. 2001).
Inhibition of tomato proteases by EPI1 and EPI10 could form a novel type of
defense-counterdefense mechanism between plants and microbial pathogens. EPI1 and
EPI10 are extracellular protease inhibitors, which inhibited and interacted with the
pathogenesis-related P69B subtilisin-like serine protease of tomato in intercellular fluids
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