The Xylanase Inhibitor TAXI-I Increases Plant Resistance to Botrytis cinerea by Inhibiting the BcXyn11a Xylanase Necrotizing Activity

During host plant infection, pathogens produce a wide array of cell wall degrading enzymes (CWDEs) to break the plant cell wall. Among CWDEs, xylanases are key enzymes in the degradation of xylan, the main component of hemicellulose. Targeted deletion experiments support the direct involvement of the xylanase BcXyn11a in the pathogenesis ofBotrytis cinerea. Since theTriticum aestivumxylanase inhibitor-I (TAXI-I) has been shown to inhibit BcXyn11a, we verified if TAXI-I could be exploited to counteractB. cinereainfections. With this aim, we first producedNicotiana tabacumplants transiently expressing TAXI-I, observing increased resistance toB. cinerea. Subsequently, we transformedArabidopsis thalianato express TAXI-I constitutively, and we obtained three transgenic lines exhibiting a variable amount of TAXI-I. The line with the higher level of TAXI-I showed increased resistance toB. cinereaand the absence of necrotic lesions when infiltrated with BcXyn11a. Finally, in a droplet application experiment on wild-typeArabidopsisleaves, TAXI-I prevented the necrotizing activity of BcXyn11a. These results would confirm that the contribution of BcXyn11a to virulence is due to its necrotizing rather than enzymatic activity. In conclusion, our experiments highlight the ability of the TAXI-I xylanase inhibitor to counteractB. cinereainfection presumably by preventing the necrotizing activity of BcXyn11a.