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

Abstract

One-sentence summary:BXL4 is a putative bifunctional 23 xylosidase/arabinofuranisodase localising to the apoplast, important for immunity 24 against the necrotrphic pathogen B. cinerea. 25 2 ABSTRACT 26 Plant cell walls constitute physical barriers that restrict access of microbial 27 pathogens to the contents of plant cells. The primary cell wall of multicellular 28 plants predominantly consists of cellulose, hemicellulose and pectin. In 29 Arabidopsis, a cell wall-localised protein, BETA-XYLOSIDASE 4 (BXL4) that 30 belongs to a seven-member BETA-XYLOSIDASE (BXL) gene family was induced 31 upon infection with the necrotrophic fungal pathogen Botrytis cinerea and 32 mechanical wounding in a jasmonoyl isoleucine (JA-Ile) dependent manner. 33 Ectopic expression of the BXL4 gene in Arabidopsis seed coat epidermal cells 34 was able to rescue a bxl1 mutant phenotype suggesting that like BXL1, BXL4, 35 had both xylosidase and arabinosidase activity and acts in mura on cell wall 36 polysaccharides. bxl4 mutants show a compromised resistance to B. cinerea. 37 Upon infection, bxl4 mutants accumulated reduced levels of JA-Ile and 38 camalexin. Conditional overexpression of BXL4 resulted in enhanced 39 expression of PDF1.2 and PAD3 transcripts both before and after B. cinerea 40 infection. This was associated with reduced susceptibility of the transgenic lines 41 to B. cinerea. These data suggest that remodelling or degradation of one or more 42 cell wall polysaccharides is important for plant immunity against B. cinerea and 43 plays a role in pathogen-induced JA-Ile and camalexin accumulation. 44 45 48 evolved various inducible and constitutive defence mechanisms against the different 49 biotic and abiotic perturbations (Schutzendubel and Polle, 2002; Jones and Dangl, 50