Data_Sheet_1_Distribution, Function, and Evolution of a Gene Essential for Trichothecene Toxin Biosynthesis in Trichoderma.pdf

Trichothecenes are terpenoid toxins produced by species in 10 fungal genera, including species of Trichoderma. The trichothecene biosynthetic gene (tri) cluster typically includes the tri5 gene, which encodes a terpene synthase that catalyzes formation of trichodiene, the parent compound of all trichothecenes. The two Trichoderma species, Trichoderma arundinaceum and T. brevicompactum, that have been examined are unique in that tri5 is located outside the tri cluster in a genomic region that does not include other known tri genes. In the current study, analysis of 35 species representing a wide range of the phylogenetic diversity of Trichoderma revealed that 22 species had tri5, but only 13 species had both tri5 and the tri cluster. tri5 was not located in the cluster in any species. Using complementation analysis of a T. arundinaceum tri5 deletion mutant, we demonstrated that some tri5 homologs from species that lack a tri cluster are functional, but others are not. Phylogenetic analyses suggest that Trichoderma tri5 was under positive selection following its divergence from homologs in other fungi but before Trichoderma species began diverging from one another. We propose two models to explain these diverse observations. One model proposes that the location of tri5 outside the tri cluster resulted from loss of tri5 from the cluster in an ancestral species followed by reacquisition via horizontal transfer. The other model proposes that in species that have a functional tri5 but lack the tri cluster, trichodiene production provides a competitive advantage.

单端孢霉烯类毒素（Trichothecenes）是由10个真菌属的菌种产生的萜类毒素，涵盖木霉属（Trichoderma）的多个物种。单端孢霉烯生物合成基因（tri）簇通常包含tri5基因，该基因编码一种萜合酶，可催化木霉烯（trichodiene）的合成——木霉烯是所有单端孢霉烯类毒素的母源化合物。目前已研究的两个木霉属物种，即长梗木霉（Trichoderma arundinaceum）和短密木霉（T. brevicompactum），具有独特性：tri5基因位于tri簇之外的基因组区域内，且该区域不包含其他已知的tri家族基因。本研究对覆盖木霉属广泛系统发育多样性的35个物种进行分析后发现，其中22个物种携带tri5基因，仅13个物种同时拥有tri5基因与tri簇。所有木霉属物种的tri5基因均未整合至tri簇内。通过对长梗木霉tri5基因缺失突变体进行互补分析，本研究证实：部分来自无tri簇物种的tri5同源基因具有生物学功能，而另一些则无此功能。系统发育分析结果显示，木霉属的tri5基因在从其他真菌的同源基因中分化之后、且在木霉属各物种彼此分化之前，曾经历过正选择作用。针对上述多样的研究结果，本研究提出两种解释模型。第一种模型认为，tri5基因位于tri簇之外的原因是：祖先物种先从tri簇中丢失了tri5基因，随后通过水平基因转移重新获得该基因。第二种模型则提出，对于那些拥有功能性tri5基因但缺乏tri簇的物种而言，合成木霉烯的能力可为其带来竞争优势。