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Microbial Endoxylanases: Effective Weapons to Breach the Plant Cell-Wall Barrier or, Rather, Triggers of Plant Defense Systems?

October 2006 , Volume 19 , Number  10
Pages  1,072 - 1,081

Tim Beliën , 1 Steven Van Campenhout , 1 Johan Robben , 2 and Guido Volckaert 1

1Katholieke Universiteit Leuven, Laboratory of Gene Technology, Kasteelpark Arenberg 21, B-3001 Leuven, Belgium; 2Universiteit Hasselt en transnationale Universiteit Limburg, Biomedical Research Institute, Agoralaan, Gebouw A, B-3590 Diepenbeek, Belgium

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Accepted 12 June 2006.

Endo-β-1,4-xylanases (EC are key enzymes in the degradation of xylan, the predominant hemicellulose in the cell walls of plants and the second most abundant polysaccharide on earth. A number of endoxylanases are produced by microbial phytopathogens responsible for severe crop losses. These enzymes are considered to play an important role in phytopathogenesis, as they provide essential means to the attacking organism to break through the plant cell wall. Plants have evolved numerous defense mechanisms to protect themselves against invading pathogens, amongst which are proteinaceous inhibitors of cell wall-degrading enzymes. These defense mechanisms are triggered when a pathogen-derived elicitor is recognized by the plant. In this review, the diverse aspects of endoxylanases in promoting virulence and in eliciting plant defense systems are highlighted. Furthermore, the role of the relatively recently discovered cereal endoxylanase inhibitor families TAXI (Triticum aestivum xylanase inhibitor) and XIP (xylanase inhibitor protein) in plant defense is discussed.

Additional keywords: ethylene-inducing xylanase (EIX) , glycoside hydrolase (GH) , hypersensitive response (HR) , plant pathogens , signaling cascade .

© 2006 The American Phytopathological Society