Expression of a wheat xylanase inhibitor and of a Fusarium graminearum xylanase in plants increase resistance to pathogens.

During host plant infection, pathogens produce many cell wall degrading enzymes (CWDE) in order to colonize the host tissue and also to obtain nutrients. Xylanases are hydrolytic enzymes with a dual role: they catalyze the hydrolysis of xylan, the largest structural polysaccharide of plant cell wall, and some of them can cause necrosis in the host tissue. Since a wheat xylanase inhibitor (TAXI-I) has been shown to inhibit a Botrytis cinerea xylanase, a well known virulence factor of the fungus, we transiently expressed TAXI-I and TAXI-III inhibitors, which has similar inhibitory capability, in tobacco leaves by agroinfiltration. Total leaves protein extracts expressing TAXIs inhibited fungal xylanase activity and TAXIs agroinfiltrated tobacco plants were less susceptible towards B. cinerea by about 20-25%. Recently we have identified a Fusarium graminearum xylanase (FGSG_03624) shown to cause H2O2 accumulation in wheat tissues and induction of defense genes in Arabidopsis thaliana; we therefore tested its ability to increase resistance against bacterial and fungal pathogens. Exogenous treatment with the xylanase showed a slight reduction of symptoms caused by Pseudomonas syringae pv. maculicola, while the treatment was ineffective against B. cinerea. To further verify this result we also transiently expressed the xylanase in tobacco plants through agroinfiltration; preliminary infection experiments seem to confirm previous results. Finally we also produced by floral dip transformation Arabidopsis transgenic plants constitutively expressing TAXI-I, TAXI-III and the xylanase FGSG_03624. Infection experiments of these plants with B. cinerea and P. syringae pv. maculicola are in progress.