Submitted to: Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2014
Publication Date: 6/25/2014
Citation: Malmierca, M.G., Barua, J., McCormick, S.P., Izquierdo-Bueno, I., Cardoza, R.E., Alexander, N.J., Hermosa, R., Collado, I.G., Monte, E., Gutierrez, S. 2014. Novel aspinolide production by Trichoderma arundinaceum with a potential role in Botrytis cinerea antagonistic activity and plant defense priming. Environmental Microbiology. 17(4):1103-1118. Interpretive Summary: Some trichothecenes, produced by fungi that infect crops, are toxic to plants and can be harmful to the health of humans and animals that consume food or feed prepared from infected grain. A trichothecene, harzianum A (HA), produced by the biocontrol fungus Trichoderma arundinaceum, is toxic to other fungi but not to plants. HA helps Trichoderma to fight harmful plant pathogens and primes natural plant defenses to fungal attack. However, genetically blocking production of HA does not eliminate the ability of Trichoderma to control fungal pathogens. In this research, we found that when HA production is blocked, metabolism of the fungus is altered and a new metabolite, aspinolide C, is produced that also inhibits fungal pathogen growth and primes plant defenses, effectively compensating for the loss of HA. This research provides scientists with the tools to identify other factors that are important in biocontrol of other fungi and to understand the interactions between these factors and trichothecenes. Knowledge of genetic control of trichothecenes and other metabolites may aid in designing safe and effective biocontrol organisms to use against plant fungal diseases.
Technical Abstract: Harzianum A (HA), a trichothecene produced by Trichoderma arundinaceum, has recently been described to have antagonistic activity against fungal plant pathogens and to induce plant defence genes. In the present work, we have shown that a tri5 genedisrupted mutant that lacks HA production overproduces two polyketides, aspinolides B and C, which were not detected in the wild-type strain. Furthermore, four new aspinolides (D–G) were characterized. These compounds confirm that a terpene-polyketide cross-pathway exists in T. arundinaceum, and they may be responsible for the antifungal activity and the plant sensitization effect observed with the tri5- disrupted mutant. In addition, the molecular changes involving virulence factors in the phytopathogenic fungus Botrytis cinerea 98 (Bc98) during interaction with T. arundinaceum were investigated. The expression of genes involved in the production of botrydial by Bc98 was relatively repressed by HA, whereas other virulence genes of this pathogen were induced by the presence of T. arundinaceum, for example atrB and pg1 which encode for an ABC transporter and endopolygalacturonase 1 respectively. In addition, the interaction with Bc98 significantly repressed the production of HA by T. arundinaceum, indicating that a bidirectional transcriptional regulation is established between these two antagonistic fungi.