## 4 Discussion
Our analyses revealed that single-copy SQS and OSC enzymes provide the linear and cyclic precursors required for triterpene biosynthesis in most _Trichoderma_ species. However, the presence of additional SQSs indicates that pathway-specific SQSs could be present as well. In the same way, additional GGPP and FPP synthases may act as donors of terpenoid precursors in specific biosynthetic pathways in members of the clades Harzianum and Brevicompactum. This most likely reflects specific portions of the terpenoid inventory of these species and guarantees an efficient distribution of terpenoid precursors between primary and secondary metabolism. Harziandione was the first diterpene isolated from _Trichoderma_ spp. [101], and a number of these compounds have been recently reported in these species [102; 103; 104; 105; 106]. Nevertheless, the low number of diTS found here indicates that the ability of _Trichoderma_ spp. for diterpene biosynthesis is scarce and not very widespread within the genus. Interestingly, our analyses revealed that _Trichoderma_ spp. have the potential to produce sesterterpenes and indole diterpenes. Sesterterpenes are rare among terpenoids, and their antimicrobial and nematocidal properties [107] could confer competitive advantages to some _Trichoderma_ spp. On the other hand, the production of indole diterpenes has been reported in some Sordariomycetes, being involved in protecting their reproductive structures from fungivores [108]. Many of the indole diterpene-producer fungi establish symbiotic relations with plants, thus, biosynthesis of these compounds may confer ecological advantages on _Trichoderma_-host associations as well [109]. No monoTS were found among the genomes analysed in this work, although production of monoterenes has been reported in _T. virens_[27; 110]. No _bona fide_ monoTS have been identified in fungi [111], and the scarce availability of sequences of these enzymes could have led to miss-predict them. Since fungal sesquiTS are able to cyclize GPP [112], we hypothesize that monoTSs of _Trichoderma_ could be actually included within \"uncharacterized group 4\", since they are phylogenetically close to sesquiTS, and other uncharacterized proteins were found restricted to some clades not including _T. virens_ or fell into the TRI5 superfamily. We found highly conserved _tri5_ orthologs in non-trichothece-producer _Trichoderma_ species missing on the entire TRI cluster, some of which have been previously reported [113]. This leaves open some questions about the role of _tri5_ in beneficious _Trichoderma_ spp., a non-producer of trichothecens. Unlike other _tri5_-containing species, _tri5_ is embedded in a BGC in _T. gamsii_, enclosing tailoring enzymes, a TF and a transporter. The presence of a TF within the cluster suggests a pathway-specific regulation, while the presence of a transporter suggests the production of a sesquiterpenoid with extra-cellular functions. Some of these genes were likely transferred to _Trichoderma_ spp. by HGT from Eurotiomycetes, but the entire cluster is only present in _T. gamsii_, suggesting the origin of a novel _tri5_-associated BGC in this species. This cluster could lead to an uncharted trichodiene-derived sesquiterpene biosynthetic pathway, producing novel metabolites with potential agronomic interest. Since _tri5_ seems to be functionally associated to two different BGCs (TRI and that found in _T. gamsii_), we hypothesize this sesquiTS is involved in different metabolic pathways in _Trichoderma_. The striking genomic potential for terpenoid production of _Trichoderma_ spp. found in this work suggests that functional differentiation of gene family members is the driver for the high TS gene numbers of these species. Here we provide a picture showing that different TS genes are differentially regulated, a strong indication of different biological functions. Availability of C source had contrasting effects on the expression of TS genes, as observed in SMs genes from other fungi [57; 114].