The 18mer peptaibols from Trichoderma virens elicit plant defence responses

Abstract

SUMMARY Peptaibols, the products of non-ribosomal peptide synthetases (NRPS), are linear peptide antibiotics produced by Trichoderma and other fungal genera. Trichoderma virens strain Gv29-8, a well-known biocontrol agent and inducer of plant defence responses, produces three lengths of peptaibols, 11, 14 and 18 residues long, with several isoforms of each. Disruption of the NRPS gene, tex1, encoded by a 62.8-kb uninterrupted open reading frame, results in the loss of production of all forms of 18-residue peptaibols. Tex1 is expressed during all Trichoderma developmental stages (germinating conidia, sporulating and non-sporulating mycelia) examined on solid media. Expression analysis by reverse transcriptase PCR shows that in Gv29-8 wild-type the abundance of tex1 transcript is greater during co-cultivation with cucumber seedling roots than when grown alone. Cucumber plants co-cultivated with T. virens strains disrupted in tex1 show a significantly reduced systemic resistance response against the leaf pathogen Pseudomonas syringae pv. lachrymans, and reduced ability to produce phenolic compounds with inhibitory activity to the bacteria as compared with plants grown in the presence of wild-type. Two synthetic 18-amino-acid peptaibol isoforms (TvBI and TvBII) from Gv29-8 when applied to cucumber seedlings through the transpiration stream can alone induce systemic protection to the leaf pathogenic bacteria, induce antimicrobial compounds in cucumber cotyledons and up-regulate hydroxyperoxide lyase (hpl), phenylalanine ammonia lyase (pal1) and peroxidase (prx) gene expression. These data strongly suggest that the 18mer peptaibols are critical in the chemical communication between Trichoderma and plants as triggers of non-cultivar-specific defence responses.

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.…”

“…Fungal mutualists confer a wide range of benefits to their hosts (Porras-Alfaro & Bayman, 2011), including enhanced host disease resistance (Djonović et al, 2007;Pozo & Azcó nAguilar, 2007;Viterbo et al, 2007), drought tolerance (Hause & Fester, 2005), improved nutrient uptake and Trichoderma NRPSs growth (Balestrini & Lanfranco, 2006;Martin et al, 2007;Chacó n et al, 2007), and protection against invertebrate and vertebrate herbivory (Clay & Schardl, 2002). The expression of induced defences is mediated by complex signalling networks in which the plant hormones JA and SA play key roles (Smith et al, 2009).…”

“…Root colonization by Trichoderma spp. also induces other components of the ISR mechanism, namely the genes hpl, aos and peroxidase (prx) (Viterbo et al, 2005(Viterbo et al, , 2007Vargas et al, 2008). T. virens induces ISR, but not SAR responses in maize; mutants of T. virens lacking the elicitor protein SM1 failed to induce ISR responses (Djonović et al, 2007).…”

“…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).…”

Phylogenomic analysis of polyketide synthase-encoding genes in Trichoderma

“…are probably best known for their production of peptaibols, which are non-ribosomal peptides with antimicrobial and plant defence-stimulating activity (Viterbo et al, 2007). Relatively less studied in Trichoderma are PKSs.…”