A cytochrome P450 monooxygenase gene required for biosynthesis of the trichothecene toxin harzianum A in Trichoderma

Authors: CARDOZA, ROSA - University Of Leon; McCormick, Susan; LINDO, LAURA - University Of Leon; Kim, Hye-Seon; OLIVERA, ELIAS - University Of Leon; NELSON, DAVID - University Of Tennessee; Proctor, Robert; GUTIERREZ, SANTIAGO - University Of Leon

Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2019
Publication Date: 8/5/2019
Citation: Cardoza, R.E., McCormick, S.P., Lindo, L., Kim, H.-S., Olivera, E.R., Nelson, D.R., Proctor, R.H., Gutierrez, S. 2019. A cytochrome P450 monooxygenase gene required for biosynthesis of the trichothecene toxin harzianum A in Trichoderma. Applied Microbiology and Biotechnology. 103(19):8087-8103. https://doi.org/10.1007/s00253-019-10047-2.
DOI: https://doi.org/10.1007/s00253-019-10047-2

Interpretive Summary: Trichothecenes are a group of fungal toxins (mycotoxins) that when present in crops a pose health risks to people, pets, and livestock. Trichothecenes are diverse in structure and are produced by diverse fungi, including some that threaten agriculture and others that benefit agriculture. For example, the fungus Fusarium graminearum causes head blight of cereal crops and produces the trichothecene deoxynivalenol, which is phytotoxic and contributes to the ability of the fungus to cause head blight. In contrast, the fungus Trichoderma arundinaceum inhibits growth of multiple plant-disease-causing fungi and produces the trichothecene harzianum A, which has low phytotoxicity but high fungal toxicity. In this study, we identified a gene in T. arundinaceum that is required for synthesis of the part of harzianum A that reduces its phytotoxicity. The gene also occurs in other harzianum A-producing Trichoderma species, but not in other fungi that produce trichothecenes with structural features similar to the part of harzianum A that reduces phytotoxicity. These results provide information on genetic mechanisms in fungi that are responsible for synthesis of trichothecenes that differ in phytotoxicity. The information will aid development of methods to counteract the phytotoxic effects of trichothecenes and, thereby, the plant-disease-promoting effects of the toxins. Such methods will help control crop diseases caused by trichothecene-producing fungi and reduce trichothecene contamination in crops.

Technical Abstract: Trichothecenes are sesquiterpene toxins produced by diverse fungi, including some species of Trichoderma that are potential plant disease biocontrol agents. Trichoderma arundinaceum produces the trichothecene harzianum A (HA), which consists of the core trichothecene structure (12,13-epoxytrichothec-9-ene, EPT) with a linear polyketide-derived substituent (octa-2,4,6-trienedioyl) esterified to an oxygen at carbon atom 4. The genes required for biosynthesis of EPT and the eight-carbon polyketide precursor of the octa-2,4,6-trienedioyl substituent, as well as for esterification of the substituent to EPT have been described. However, genes required for conversion of the polyketide (octa-2,4,6-trienoic acid) to octa-2,4,6-trienedioyl-CoA, the immediate precursor of the substituent, have not been described. Here, we identified 91 cytochrome P450 monooxygenase genes in the genome sequence of T. arundinaceum, and provide evidence from gene deletion, complementation, cross-culture feeding, and chemical analyses that one of them (tri23) is required for conversion of octa-2,4,6-trienoic acid to octa-2,4,6-trienedioyl-CoA. The gene was detected in other HA-producing Trichoderma species, but not in species of other fungal genera that produce trichothecenes with an octa-2,4,6-trienoic acid-derived substituent. These findings indicate that tri23 is a trichothecene biosynthetic gene unique to Trichoderma species, which in turn suggests that modification of octa-2,4,6-trienoic acid during trichothecene biosynthesis has evolved independently in some fungi.