Date Published: April 17, 2018
Publisher: Springer Berlin Heidelberg
Author(s): Xuping Shentu, Jiayi Yao, Xiaofeng Yuan, Linmao He, Fan Sun, Kozo Ochi, Xiaoping Yu.
Trichoderma brevicompactum and T. arundinaceum both can synthesize trichodermin with strong antifungal activity and high biotechnological value. The two Trichoderma species have a tri cluster, which includes seven genes (tri14, tri12, tri11, tri10, tri3, tri4, and tri6) that encode transport and regulatory enzymes required for the biosynthesis of trichodermin. Here, we isolated T. brevicompactum 0248 transformants with disrupted tri11, tri4, or tri3 gene. We also described the effect of tri11, tri3, or tri4 deletion on the expression of other genes in the tri cluster. Targeted Δtri3 knockout mutant exhibited a sharp decline in the production of trichodermin, and trichodermol, which is a substrate for trichodermin production, accumulated. Thus, the results demonstrated that tri3 was responsible for the biosynthesis of trichodermin, and the tri3 gene-encoded enzyme catalyzed the acetylation reaction of the hydroxy group at C-4 of the trichodermin skeleton. In addition, tri4 and tri11 deletion mutants were generated to evaluate the roles of tri4 and tri11 in trichodermin biosynthesis, respectively. Deletion mutant strain Δtri4 or Δtri11 did not produce trichodermin in T. brevicompactum, indicating that tri4 and tri11 are essential for trichodermin biosynthesis. This is the first to report the function of tri3, tri4 and tri11 in T. brevicompactum, although the role of tri4 and tri11 has already been described for T. arundinaceum by Cardoza et al. (Appl Environ Microbiol 77:4867–4877, 2011).
Trichoderma species are well-known biological control agents of diseases in numerous crops, and these species produce many antifungal compounds and cell-wall-degrading enzymes (Harman 2006; Malmierca et al. 2012; Tijerino et al. 2011a, b). The biocontrol activities of Trichoderma spp. against phytopathogenic fungi generally include antibiosis, parasitism, and competition for space and nutrients (Harman 2006). Antibiotic molecules synthesized by Trichoderma are low-molecular-weight and volatile metabolites as well as high-molecular weight polar metabolites. The former type includes simple aromatic compounds, polyketides, volatile terpenes, and isocyanide metabolites, while the latter includes peptaibols and diketopiperazine-like gliotoxin and gliovirin compounds (Reino et al. 2008; Szekeres et al. 2005; Tijerino et al. 2011a). Trichothecenes belong to a large group of terpenoid-derived secondary metabolites and are mainly synthesized by Fusarium and other fungal genera, such as Trichoderma, Myrothecium, Spicellum, Stachybotrys, and Trichothecium (Shentu et al. 2014a; Wilkins et al. 2003). Terpenes are derived from the repetitive fusion of branched five-carbon units based on an isopentane skeleton, and most of the chemical intermediates in their biosynthetic pathway have been identified (Tijerino et al. 2011b). The trichothecene biosynthetic pathway in Fusarium has been documented and extensively reviewed (Kimura et al. 2007). However, the genes involved in trichothecene biosynthesis in the other genera remain unknown.
Trichoderma is an interesting fungus because of its important application in biocontrol (Malmierca et al. 2012). However, T. brevicompactum has not been well-studied among Trichoderma, because T. brevicompactum (IBT 9471) had been erroneously considered as T. harzianum (ATCC 90237) because of substantial shared micromorphology of these two species (Nielsen et al. 2005; Degenkolb et al. 2008). Until 2005, this IBT 9471 strain has been reclassified as T. brevicompactum on the basis of phylogenetic lineage within the morphological species T. brevicompactum and trichothecene production (Nielsen et al. 2005; Shentu et al. 2014a). Previous studies reported that T. brevicompactum is one of the Trichoderma species that produces trichodermin, which exhibits strong antifungal activity and has high biotechnological value (Tijerino et al. 2011a, b). Therefore, conducting systematic studies on this species is necessary and urgent.