Abstract
Trichoderma harzianum is a filamentous fungus well adapted to different ecological niches. Owing to its ability to antagonize a wide range of plant pathogens, it is used as a biological control agent in agriculture. Selected strains of T. harzianum are also able to increase the tolerance of plants to biotic and abiotic stresses. However, little is known about the regulatory elements of the T. harzianum transcriptional machinery and their role in the biocontrol by this species. We had previously reported the involvement of the transcription factor THCTF1 in the T. harzianum production of the secondary metabolite 6-pentyl-pyrone, an important volatile compound related to interspecies cross-talk. Here, we performed a subtractive hybridization to explore the genes regulated by THCTF1, allowing us to identify a multiprotein bridging factor 1 (mbf1) homolog. The gene from T. harzianum T34 was isolated and characterized, and the generated Thmbf1 overexpressing transformants were used to investigate the role of this gene in the biocontrol abilities of the fungus against two plant pathogens. The transformants showed a reduced antifungal activity against Fusarium oxysporum f. sp. lycopersici race 2 (FO) and Botrytis cinerea (BC) in confrontation assays on discontinuous medium, indicating that the Thmbf1 gene could affect T. harzianum production of volatile organic compounds (VOC) with antifungal activity. Moreover, cellophane and dialysis membrane assays indicated that Thmbf1 overexpression affected the production of low molecular weight secreted compounds with antifungal activity against FO. Intriguingly, no correlation in the expression profiles, either in rich or minimal medium, was observed between Thmbf1 and the master regulator gene cross-pathway control (cpc1). Greenhouse assays allowed us to evaluate the biocontrol potential of T. harzianum strains against BC and FO on susceptible tomato plants. The wild type strain T34 significantly reduced the necrotic leaf lesions caused by BC while plants treated with the Thmbf1-overexpressing transformants exhibited an increased susceptibility to this pathogen. The percentages of Fusarium wilt disease incidence and values of aboveground dry weight showed that T34 did not have biocontrol activity against FO, at least in the ‘Moneymaker’ tomato variety, and that Thmbf1 overexpression increased the incidence of this disease. Our results show that the Thmbf1 overexpression in T34 negatively affects its biocontrol mechanisms.
Highlights
Trichoderma is a genus of filamentous fungi distributed worldwide, extremely well suited to live in different ecological niches (Druzhinina et al, 2011)
The disease of tomato plants appears to be influenced by the method of inoculation of T. harzianum, taken all together, these results indicate that strain T34 did not show a biocontrol activity against FO in ‘Moneymaker’ plants, and that Thmbf1 overexpression in T34 reduced its antifungal activity against FO, leading to increased Fusarium wild disease
multiprotein bridging factor 1 (MBF1) proteins control different physiological and/or developmental processes and, few studies have been reported in fungi, they have been related to virulence in B. bassiana and M. oryzae (Ying et al, 2014; Fan et al, 2017)
Summary
Trichoderma is a genus of filamentous fungi distributed worldwide, extremely well suited to live in different ecological niches (Druzhinina et al, 2011). This is due to its remarkably diverse metabolism, capable of catabolising a broad variety of substrates as well as of producing a huge diversity of secondary metabolites (Mukherjee et al, 2013). Members of the highly conserved multiprotein bridging factor 1 (MBF1) protein family function as non-DNAbinding transcriptional coactivators. These mediator proteins are involved in regulating metabolic and developmental pathways in different organisms ranging from fungi to animals (Li et al, 1994; Takemaru et al, 1997). The potato MBF1 protein is induced in response to attack by a pathogen (Godoy et al, 2001) as well as to heat and oxidative stresses (Arce et al, 2006)
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