Analysis of a putative glycosylation site in the Trichoderma virens elicitor SM1 reveals no role in protein dimerization

The biocontrol fungus Trichoderma virens is an avirulent symbiont with the ability to control plant disease through the production of antibiotic compounds, induction of plant resistance to pathogens, and mycoparasitism of other fungi. Previous research has shown that resistance to plant pathogens in maize is induced by the secretion of a member of the cerato-platanin family of proteins, sm1, and that only the monomer of this protein has this activity. It has been hypothesized that glycosylation of sm1 disrupts dimer formation and keeps sm1 in this active monomer form. To further understand the role of this putative glycosylation site as a mechanism to prevent dimerization and subsequent elicitor activity, a point mutation was created in sm1 and transformed into a sm1 deletion strain. Analysis of the behavior of the altered protein (PTM) demonstrates that the putative glycosylation site is not involved in protein dimerization and deletion of this site does not prevent the protein from testing positive for glycosylation. We propose that SM1 is not glycosylated but instead may interact with an oligosaccharide or other small molecule. However, the exact mechanism of dimerization in SM1 remains unknown. •In previous work, a putative glycosylation site was predicted to prevent dimerization in the ISR elicitor SM1 .•A point mutation was constructed at the site of this putative glycosylation .•The mutated SM1(PTM) showed no increase dimerization, even over extended time .•Glycosylation staining was similar between SM1 and PTM .•Periodic acid/Schiff staining indicated that SM1 may not be glycosylated .•The putative glycosylation site in SM1 is not involved in its biological activity .