Sm1, a Proteinaceous Elicitor Secreted by the Biocontrol Fungus Trichoderma virens Induces Plant Defense Responses and Systemic Resistance

Abstract

The soilborne filamentous fungus Trichoderma virens is a biocontrol agent with a well-known ability to produce antibiotics, parasitize pathogenic fungi, and induce systemic resistance in plants. Even though a plant-mediated response has been confirmed as a component of bioprotection by Trichoderma spp., the molecular mechanisms involved remain largely unknown. Here, we report the identification, purification, and characterization of an elicitor secreted by T. virens, a small protein designated Sm1 (small protein 1). Sm1 lacks toxic activity against plants and microbes. Instead, native, purified Sm1 triggers production of reactive oxygen species in monocot and dicot seedlings, rice, and cotton, and induces the expression of defense-related genes both locally and systemically in cotton. Gene expression analysis revealed that SM1 is expressed throughout fungal development under different nutrient conditions and in the presence of a host plant. Using an axenic hydroponic system, we show that SM1 expression and secretion of the protein is significantly higher in the presence of the plant. Pretreatment of cotton cotyledons with Sm1 provided high levels of protection to the foliar pathogen Colletotrichum sp. These results indicate that Sm1 is involved in the induction of resistance by Trichoderma spp. through the activation of plant defense mechanisms.

Functional analysis of non-ribosomal peptide synthetases (NRPSs) in Trichoderma virens reveals a polyketide synthase (PKS)/NRPS hybrid enzyme involved in the induced systemic resistance response in maize

“…Understanding the mechanisms of induced resistance and identifying novel elicitors would greatly enhance our capability to commercially exploit this eco-friendly approach to plant disease management . Even though the phenomenon of Trichoderma-mediated induced resistance has been known for more than a decade, only a few elicitor molecules such as the 18-residue peptaibol (Tex1) and SM1 have been identified (Viterbo et al, 2007;Djonović et al, 2006). The recent genome sequencing of T. virens enabled the identification and high-throughput analysis of genes encoding NRPSs.…”

“…Root inducibility of the NRPSs was determined in a hydroponic system containing maize seedlings as described previously (Djonović et al, 2006). Maize seeds (Silver Queen hybrid) were surface-disinfected with 10 % H 2 O 2 for 2 h, rinsed with distilled water, and placed in moist chambers for 3 days for germination.…”

“…Trichoderma-secreted xylanase, cellulase and swollenin induce localized plant reactions and necrosis (see Shoresh et al, 2010). SM1 is a hydrophobic, small, cysteine-rich, secreted protein and one of the most well-characterized elicitor-like proteins secreted by T. virens (Djonović et al, 2006(Djonović et al, , 2007Vargas et al, 2008;Buensanteai et al, 2010). Two other well-characterized elicitors are the non-ribosomal peptides alamethicin (T. viride) and the 18-residue peptaibols Tex1 (T. virens) (Leitgeb et al, 2007;Viterbo et al, 2007).…”

Pythium oligandrum: an example of opportunistic success

“…Such oligosaccharides, originating from the prey cell walls, appear to be essential for stimulating Trichoderma growth and triggering the production of antibiotics and lytic enzymes in addition to acting as elicitors of the plant defence response (Vinale et al, 2008). Apart from oligosaccharides, other molecules such as peptaibols are thought to contribute to the activation of the plant defence strategy by Trichoderma species (Benítez et al, 2004;Djonović et al, 2006). The data on the ability of Trichoderma species to produce an array of potential elicitors raise the question about the extent to which the enzymes secreted by P. oligandrum are involved in the release of molecules with potent elicitor activity.…”

Cerato-platanin shows expansin-like activity on cellulosic materials

“…These proteins are grouped into a protein family of which CP is the first member (the "cerato-platanin family", Pfam PF07249), and like CP some of them are known for the resistance-inducing activity in plants (Djonović et al 2006;Frías et al 2011;Seidl et al 2006;Yang et al 2009;Zaparoli et al 2009). In the "ceratoplatanin family", the molecular mechanism of action on plants and above all the biological role in fungal life are little-known aspects.…”