The expression of TAXI-I and TAXI-III xylanase inhibitors and of a Fusarium graminearum xylanase increases plant resistance to bacterial and fungal pathogens

During host plant infection, pathogens produce a wide range 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 cell wall component of commelinoid monocot plants. Fungal xylanases can also induce necrosis in plants, as shown for the Botrytis cinerea Xyn11A xylanase, a well-known virulence factor of this fungus. Since the Triticum aestivum Xylanase Inhibitor-I (TAXI-I) has been shown to inhibit the B. cinerea Xyn11A, we verified if TAXI-I and TAXI-III, another TAXI type xylanase inhibitor with similar inhibitory specificity, can be exploited to counteract B. cinerea infections. With this aim, we transiently expressed TAXIs in tobacco leaves by agroinfiltration and produced Arabidopsis thaliana constitutively expressing transgenic plants. TAXIs agroinfiltrated tobacco plants showed a 20-25% reduction in symptoms caused by B. cinerea. This efficacy was confirmed also by B. cinerea infection experiments of TAXI-III transgenic line (20-25% symptoms reduction). Conversely, TAXI-I transgenic line did not show increased resistance to B. cinerea. Since the Fusarium graminearum xylanase FGSG_03624 has been shown to induce defense responses in A. thaliana independently from its enzymatic activity, we also tested its ability to increase resistance against bacterial and fungal pathogens by transient expression and transgenic approach. Arabidopsis transgenic lines expressing an inactivated form of FGSG_03624 showed about 20% reduction of symptoms by Pseudomonas syringae pv. maculicola, while no symptoms reduction was observed against B. cinerea. The efficacy in reducing (by about 45%) symptoms caused by P. syringae pv. tabaci was also confirmed by transient expression in tobacco through agroinfiltration.