Effect of deletion of a trichothecene toxin regulatory gene on the secondary metabolism transcriptome of the saprophytic fungus Trichoderma arundinaceum

Authors: LINDO, L - University Of Leon; McCormick, Susan; CARDOZA, R - University Of Leon; Brown, Daren; Kim, Hye-Seon; ALEXANDER, NANCY - Retired ARS Employee; Proctor, Robert; GUTIERREZ, S - University Of Leon

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2018
Publication Date: 9/5/2018
Citation: Lindo, L., McCormick, S.P., Cardoza, R.E., Brown, D.W., Kim, H.-S., Alexander, N.J., Proctor, R.H., Gutierrez, S. 2018. Effect of deletion of a trichothecene toxin regulatory gene on the secondary metabolism transcriptome of the saprophytic fungus Trichoderma arundinaceum. Fungal Genetics and Biology. 119:29-46. https://doi.org/10.1016/j.fgb.2018.08.002.
DOI: https://doi.org/10.1016/j.fgb.2018.08.002

Interpretive Summary: Some trichothecenes produced by fungi that infect cereal plants are toxic to plants and can be harmful to the health of humans and animals that consume food or feed prepared from infected grain. Other trichothecenes, such as those produced by the biocontrol fungus Trichoderma arundinaceum, are toxic to harmful fungal pathogens but not to plants. In this research, we discovered 42 gene clusters that control production of other secondary metabolites in T. arundinaceum, and found that knocking out a regulatory gene stopped production of trichothecenes and altered the expression of other secondary metabolite genes. Knowledge of genetic control of trichothecenes and other secondary metabolites may aid in designing safe and effective biocontrol organisms to use against plant fungal diseases.

Technical Abstract: Trichothecenes are terpenoid toxins produced by multiple fungal species with diverse lifestyles. In these fungi, the trichothecene biosynthetic gene (TRI) cluster encodes a Cys2His2 Zn-finger protein, and analyses of plant pathogenic Fusarium species indicate that TRI6 regulates TRI gene expression. Here, we analyzed Tri6 function in the saprophytic fungus Trichoderma arundinaceum, which produces the antimicrobial trichothecene harzianum A (HA). Deletion of the Tri6-encoding gene, TRI6, blocked HA production and reduced expression of TRI genes and early mevalonate pathway genes required for synthesis of farnesyl diphosphate (FPP), the primary metabolite that feeds into trichothecene biosynthesis. In contrast, TRI6 deletion did not affect expression of late mevalonate pathway genes required for synthesis of ergosterol from FPP, but did increase ergosterol production, perhaps because increased levels of FPP were available for ergosterol synthesis in the absence of trichothecene production. RNA-seq analyses indicated that genes in 10 of 49 secondary metabolite (SM) biosynthetic gene clusters in T. arundinaceum exhibited reduced expression and four exhibited increased expression in a TRI6 deletion mutant. Despite the metabolic and transcriptional changes, TRI6 mutants were not reduced in their ability to inhibit growth of fungal plant pathogens. Our results indicate that T. arundinaceum Tri6 regulates expression of both TRI and early mevalonate pathway genes in a manner similar to Fusarium Tri6. It remains to be determined whether the effects of TRI6 deletion on expression of other SM clusters resulted because Tri6 can bind to promoter regions in the clusters or because trichothecene production affects other SM pathways.