Multiple faces of Fusarium oxysporum effector protein Avr2

Plant pathogens, and specifically fungi, form a major threat for our crops. Fusarium oxysporum (Fo), belonging to the top ten fungal pathogens, causes vascular wilt disease in over 120 different species. This study focuses on the interaction between tomato and Fusarium oxysporum f.sp. lycopersici (Fol). First, the role of the major phytohormones, including salicylic acid (SA), ethylene (ET) and jasmonic acid (JA) for the interaction between Fol and tomato was investigated. Second, like other pathogens Fol produces effector proteins to support parasitism. Although the activities of a limited number of intracellular bacterial effectors have been analyzed in some detail, our understanding of the function of secreted fungal effectors is underexplored and incomplete. Here I show that the Avr2 effector protein, secreted by Fol during colonization of the xylem vessels, acts inside host cells. Its uptake by the plant was shown to be a non host-autonomous event and dependent on the presence of a pathogen. Furthermore, I discovered that Avr2 targets an evolutionary conserved immune pathway; Avr2 transgenic plants become hyper-susceptible to a range of bacterial and fungal pathogens. The intracellular immune-perturbing activity for this effector fits its intracellular recognition by the tomato I-2 resistance protein. The subsequent determination of the crystal structure of Avr2 allowed me to uncouple virulence from I-2-mediated immune activation, showing that they are distinct activities. These studies advance our understanding of the molecular mechanism underlying host manipulation and effector recognition, and allowed us to propose novel strategies to combat pathogens.