Trichoderma harzianum T1A constitutively secretes proteins involved in the biological control of Guignardia citricarpa

Citrus Black Spot caused by the fungus Guignardia citricarpa has an enormous economic impact. However, studies addressing the reduction or replacement of conventional fungicides for its control are scarce. Trichoderma harzianum is the most widely used species as a biological control agent. Nevertheless, only scarce reports describe the antagonism between T. harzianum and G. citricarpa. To investigate the mechanisms involved in the control of G. citricarpa, the proteins present in the secretome of T. harzianum T1A grown in medium containing deactivated mycelium of G. citricarpa were characterized and compared to a control condition. From the 178 significantly differentially expressed spots, 65 proteins were identified by mass spectrometry. Glycoside hydrolases, an L-amino acid oxidase, a serine protease and Epl 1 protein, represent 54% of the total proteins and are related not only to mycoparasitism, but also to plant defense response stimulation and biological control. When challenged by the pathogen, T. harzianum T1A reduces the total amount of secreted proteins, especially related to primary metabolism, increasing the secretion of proteins related to fungal interaction. Our results show, for the first time, that T. harzianum T1A secretes proteins related to the control of G. citricarpa, and induction of plant resistance, even in the absence of pathogen challenge.