Abstract Detail

Host/Plant Pathogen Interactions and Plant Health Management

Adams, Catharine [1], Pringle, Anne [2], Zimmerman, Kolea [3], Fenstermacher, Kristi [4], Geiser, David [5].

Mechanisms of capsaicin tolerance in fungal seed pathogens of wild chili peppers.

To deter herbivores and pathogens, many plants produce secondary metabolites. However, herbivores and pathogens that commonly associate with plants can evolve resistance to defensive compounds. Such co-evolution is evident in a wild chili pepper, Capsicum chacoense. Though plant-produced capsaicinoids slow fungal growth, fungi that infect C. chacoense seeds possess much higher capsaicinoid tolerance than other tested microbes. Previous researchers have proposed two separate mechanisms of capsaicin inhibition. A small number of studies propose that capsaicinoids can cause cell membrane disruption, while a separate, larger body of literature has demonstrated that capsaicinoids like capsaicin and dihydrocapsaicin bind to the NADH dehydrogenase (Complex I) of the Electron Transport Chain (ETC), crippling Oxidative Phosphorylation (OXPHOS) and subsequent energy production (ATP). Here, we investigated how fungal seed pathogens of wild Capsicum chacoense evolved tolerance to capsaicin. We measured fungal growth rate in the presence of different ETC inhibitors to determine 1) if these fungi possess alternative respiratory enzymes, and 2) if capsaicinoids’ effects on the ETC fully explained the effect of these inhibitors. We selected 16 fungal isolates from four Ascomycete genera (Alternaria, Colletotrichum, Fusarium and Phomopsis). In all isolates, we found evidence for a Complex I alternative NADH dehydrogenase. Unexpectedly, we also found evidence for a Complex III alternative cytochrome oxidase in many isolates. These fungi may achieve additional capsaicin tolerance by degrading capsaicin and using an ABC-drug transporter to transfer the compound out of their cells. Inhibition of OXPHOS appears to weakly explain the mechanism by which dihydrocapsaicin slows fungal growth, but not capsaicin. We hypothesize capsaicin disrupts cell and mitochondrial membranes in addition to inhibiting OXPHOS. Our research also suggests alternative respiratory enzymes are more prevalent in plant pathogens than was previously appreciated.

1 - University of California Berkeley, Plant and Microbial Biology, 321 Koshland Hall, UC Berkeley, Berkeley, CA, 94720, USA
2 - University of Wisconsin-Madison, Department of Botany and Bacteriology, Madison, WI, 53706, USA
3 - Harvard University, Organismal and Evolutionary Biology, 16 Divinity Ave, Harvard University, Cambridge, MA, 02138, USA
4 - Pennsylvania State University, Department of Plant Pathology and Environmental Microbiology, 121 Buckhout Lab, University Park, PA, 16802, USA
5 - Pennsylvania State University, Department of Plant Pathology and Environmental Microbiology, 121 Buckhout Lab, Department of Plant Pathology and Environmental Mi, University Park, PA, 16802, United States

Keywords:
Ascomycota
Alternaria
capsaicin
Capsicum chacoense
co-evolution
complex I
Colletotrichum
energy
Fusarium
glycolysis
ITS
NADH
membrane
mitochondria
Neurospora
OXPHOS
Phomopsis
Respiration
secondary metabolites
seed predation.

Presentation Type: Poster:Posters for Topics
Session: P
Location: Hall D/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 5:30 PM
Number: PPA022
Abstract ID:818
Candidate for Awards:None