Fungal xylanase inhibitor. Possesses competitive inhibiting activity against several fungal endo-1,4-beta-D-xylanases belonging to glycoside hydrolase family 10 (GH10) and family 11 (GH11). May function in plant defense against secreted fungal pathogen xylanases. Is similar to class III chitinases, but does not exhibit chitinase activity. Binds to fungal GH10 xylanases. Induced by wounding and methyl jasmonate in roots. Belongs to the glycosyl hydrolase 18 family. Xylanase inhibitor subfamily.