Fusarium graminearum produces different xylanases causing host cell death that is prevented by the xylanase inhibitors XIP-I and TAXI-III in wheat

tTo shed light on the role of Xylanase Inhibitors (XIs) during Fusarium graminearum infection, we firstdemonstrated that three out of four F. graminearum xylanases, in addition to their xylan degrading activity,have also the capacity to cause host cell death both in cell suspensions and wheat spike tissue.Subsequently, we demonstrated that TAXI-III and XIP-I prevented both the enzyme and host cell deathactivities of F. graminearum xylanases. In particular, we showed that the enzymatic inhibition by TAXI-IIIand XIP-I was competitive and only FGSG 11487 escaped inhibition.The finding that TAXI-III and XIP-I prevented cell death activity of heat inactivated xylanases and thatXIP-I precluded the cell death activity of FGSG 11487 – even if XIP-I does not inhibit its enzyme activity– suggests that the catalytic and the cell death activities are separated features of these xylanases.Finally, the efficacy of TAXI-III or XIP-I to prevent host cell death caused by xylanases was confirmedin transgenic plants expressing separately these inhibitors, suggesting that the XIs could limit F. gramin-earum infection via direct inhibition of xylanase activity and/or by preventing host cell death.