Proteomic Analysis of the Fusarium graminearum Secretory Proteins in Wheat Apoplast Reveals a Cell-Death-Inducing M43 Peptidase

<i>Fusarium graminearum</i>, a highly destructive fungal pathogen, poses a major threat to wheat production. The apoplast is an important space for plant-pathogen interactions. However, no studies have been reported on the secretory proteins of <i>F. graminearum</i> in the wheat apoplast. In this study, we performed mass spectrometry analysis of <i>F. graminearum</i> secretory proteins in wheat apoplast and identified 79 potential secretory proteins. We identified a metalloprotease (referred to as Fg28) and demonstrated its capacity to induce cell death and reactive oxygen species (ROS) accumulation in <i>Nicotiana benthamiana</i>. Fg28 is strongly up-regulated in the early stages of infection and is secreted into the intercellular space of wheat cells. Full-length Fg28 is required to induce cell death in <i>N. benthamiana</i>. In addition, Fg28 induces an immune response that is independent of BAK1/SOBIR1 and EDS1/PAD4. Furthermore, knocking out <i>Fg28</i> had no effect on morphology or pathogenicity. In conclusion, we have identified a set of <i>F. graminearum</i> secreted proteins in the wheat apoplast and a metalloproteinase that triggers immune response, providing new insights into understanding the interaction between <i>F. graminearum</i> and wheat.