The Fusarium graminearum FGSG_03624 xylanase primes plant immune responses and increases plant disease resistance

Plants activate defense responses against pathogens once pattern recognition receptors (PRRs) perceive the presence of pathogen-associated molecular patterns (PAMPs). Some cell wall degradating enzymes function as PAMPs and activate the plant immune responses, as shown for EIX and Xyn11A xylanases of Trichoderma viride and Botrytis cinerea, respectively. Since the Fusarium graminearum FGSG_03624 xylanase has been shown to induce necrosis and hydrogen peroxide accumulation in wheat independently from its enzymatic activity, we investigated its ability to modulate plant immunity. To this aim, we transiently and constitutively expressed an enzymatically inactivated form of FGSG_03624 in tobacco and Arabidopsis, respectively. Afterwards, these plants were challenged with Pseudomonas syringae pv. maculicola and B. cinerea. Effectiveness in reducing symptoms caused by the bacterial pathogen was evident both in Arabidopsis and in tobacco whilst no symptoms reduction was observed after B. cinerea infection. The increased resistance of Arabidopsis plants to P. syringae was associated to a faster and stronger activation of jasmonate/ethylene and salicylate pathways detected after pathogen inoculation. The priming effect was also confirmed after F. graminearum inoculation of durum wheat spikes exogenously treated with the FGSG_03624 xylanase. Indeed, wheat spikes treated with the xylanase exhibited reduced symptoms in the early phases of infection and a lower fungal biomass accumulation in semolina compared to control. Besides, callose deposition was detected in infected spikes previously treated with the xylanase and not in infected control plants. In conclusion, our results highlight the ability of FGSG_03624 to prime defense responses in plants thus conferring disease resistance.