The cell-wall-localised BETA-XYLOSIDASE 4 contributes to immunity of Arabidopsis against Botrytis cinerea

Plant cell walls constitute physical barriers that restrict access of microbial pathogens to the contents of plant cells. The primary cell wall of multicellular plants predominantly consists of cellulose, hemicellulose and pectin. In Arabidopsis, a cell wall-localised protein, BETA-XYLOSIDASE 4 (BXL4) that belongs to a seven-member BETA-XYLOSIDASE (BXL) gene family was induced upon infection with the necrotrophic fungal pathogen and mechanical wounding in a jasmonoyl isoleucine (JA-Ile) dependent manner. Ectopic expression of the BXL4 gene in Arabidopsis seed coat epidermal cells was able to rescue a mutant phenotype suggesting that like BXL1, BXL4, had both xylosidase and arabinosidase activity and acts on cell wall polysaccharides. mutants show a compromised resistance to Upon infection, mutants accumulated reduced levels of JA-Ile and camalexin. Conditional overexpression of resulted in enhanced expression of and transcripts both before and after infection. This was associated with reduced susceptibility of the transgenic lines to . These data suggest that remodelling or degradation of one or more cell wall polysaccharides is important for plant immunity against and plays a role in pathogen-induced JA-Ile and camalexin accumulation.