A Fusarium graminearum endo-xylanase expressed during wheat infection is a necrotizing factor.

Fusarium graminearum is the causal agent of Fusarium head blight of wheat. During the infection process, this fungus secretes a large number of hydrolytic enzymes, some of them able to degrade xylans, main constituents of monocot cell walls. In particular, endo-ß-1,4-xylanases hydrolyze the inner ß-1,4 glycosidic bond and could be important pathogenic weapons. However, xylanases could also exert effects independent from their enzymatic activity, as the case of Botrytis cinerea xylanase Xyn11A, which is also a necrotizing factor in tobacco and tomato leaves. F. graminearum gene FG03624 encodes a xylanase whose deduced amino acidic sequence has a 55% identity with Xyn11A and is one of the two most expressed endo-xylanase genes in early stages of wheat spikelets infection. We therefore cloned this gene for heterologous expression in Pichia pastoris and characterized the purified xylanase by studying its enzymatic activity in vitro and by infiltrating wheat tissues to test its necrotizing activity. Results obtained demonstrate that this endo-xylanase is able to induce cell death and production of hydrogen peroxide in the treated tissues, even when its enzymatic activity is impaired.