|Cardoza, R - University Of Leon|
|Malmierca, M - University Of Leon|
|Olivera, E - University Of Leon|
|Alexander, Nancy - Retired ARS Employee|
|Monte, E - University Of Salamanca|
|Gutierrez, S - University Of Leon|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2015
Publication Date: 9/1/2015
Publication URL: http://handle.nal.usda.gov/10113/62300
Citation: Cardoza, R.E., McCormick, S.P., Malmierca, M.G., Olivera, E.R., Alexander, N.J., Monte, E., Gutierrez, S. 2015. Effect of trichothecene production on the plant defense response and fungal physiology: overexpression of Trichoderma arundinaceum tri4 gene in T. harzianum. Applied and Environmental Microbiology. 81(18):6355-6366.
Interpretive Summary: Some trichothecenes produced by fungi that infect crop plants are toxic to plants and can be harmful to humans or animals that consume food or feed prepared from infected grain. However, the biocontrol fungus Trichoderma arundinaceum produces a trichothecene (harzianum A (HA)) that is toxic to harmful fungal pathogens. In this research we determined that chemical precursors of HA are not directly toxic to fungal pathogens but cause an increase in plant defense to infection and could thereby limit the ability of a pathogen to cause disease. These insights into the role of HA and it's precursors in biocontrol activity and plant defense response provide scientists with new tools to develop effective pathogen control strategies that promote crop production and food safety.
Technical Abstract: Trichothecenes are fungal sesquiterpenoid compounds, the majority of which have phytotoxic activity. They contaminate food and feed stocks, resulting in potential harm to animals and human beings. Trichoderma brevicompactum and T. arundinaceum produce trichodermin and harzianum A (HA), respectively, two trichothecenes that show different bioactive properties. Both compounds have remarkable antibiotic and cytotoxic activities, but in addition, trichodermin is highly phytotoxic, whileHAlacks this activity when analyzed in vivo. Analysis of Fusarium trichothecene intermediates led to the conclusion that most of them, with the exception of the hydrocarbon precursor trichodiene (TD), have a detectable phytotoxic activity which is not directly related to the structural complexity of the intermediate. In the present work, theHAintermediate 12,13-epoxytrichothec-9-ene (EPT) was produced by expression of the T.arundinaceum tri4 gene in a transgenic T. harzianum strain that already produces TD after transformation with the T. arundinaceum tri5 gene. Purified EPT did not show antifungal or phytotoxic activity, while purified HA showed both antifungal and phytotoxic activities. However, the use of the transgenic T. harzianum tri4 strain induced a ownregulation of defense-related genes in tomato plants and also downregulated plant genes involved in fungal root colonization. The production of EPT by the transgenic tri4 strain raised levels of erg1 expression and reduced squalene accumulation while not affecting levels of ergosterol. Together, these results indicate the complex interactions among trichothecene intermediates, fungal antagonists, and host plants.