The Grass is Greener in Kentucky
Symbiont Transmission and the Mutualism-Parasitism Spectrum
School of Biological Sciences
The University of Manchester
Kentucky 31 is a widely grown variety of tall fescue grass that owes its extreme stress resistance, but also its toxicity, to an endophytic fungus. It is difficult to decide where to place this symbiosis along the mutualism-parasitism spectrum. In this case study, students explore a variety of influencing factors, including partner choice, defense vs. accommodation, fitness effects on the host, and transmission of symbionts. The first three sections of the case offer lower-level undergraduate biology students an opportunity to practice hypothesis formation, scientific reasoning, and experimental planning. Students are asked to speculate about the cause of fescue toxicity before the symbiont is revealed, which then leads to an examination of defense versus partner recognition as plant responses to microbes. The fourth section of the case is appropriate for an intermediate ecology course and involves short group presentations investigating a broader range of symbioses with different transmission modes (vertical/horizontal) and microbial “services” that enhance host fitness. The final section, targeted to advanced students in research-led courses who are familiar with molecular lab techniques, requires students to write a research proposal to further investigate the nature of the fescue-endophyte interaction.
- Use scientific reasoning to form hypotheses about the cause of tall fescue toxicity, and to propose simple experiments to test these hypotheses.
- Use ecological observations to judge if a symbiont is mutualistic or parasitic.
- Describe symbiont recognition and host response to mutualists versus parasites in simple terms; discuss the link to symbiont transmission.
- Compare and contrast the fescue-endosymbiont interaction with other host-microbe interactions; discuss the range of fitness outcomes for the host.
- Develop a research question and outline an experimental approach to further dissect the fescue-endosymbiont interaction.
KeywordsEndophyte; grass; symbiosis; symbiont; mutualism; parasitism; fitness; hypothesis testing; tall fescue; Kentucky 31; fungi; fungus; microbiome; holobiont; optimal virulence
Educational LevelUndergraduate lower division, Undergraduate upper division
Type / MethodsInterrupted
Subject HeadingsBiology (General) | Ecology | Evolutionary Biology | Botany / Plant Science |
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greener_grass.pptx (~15 MB)
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The following video(s) are recommended for use in association with this case study.
- Central Concepts of Plant Pathology: The Role of Recognition in Host-Parasite Interaction
A (mostly serious) look at plant parasites, mutualists, commensalists and latent pathogens, and how plants recognize them. Running time: 5:00, or 2:08 total for recommended segments 0:48–2:02 and 2:47–3:41. Produced by Matt Pye and Tom Gordon, UC Davis, 2010.
- Mycorrhiza II – What Is It and How Does It Work?
Simplified 3D computer animation of plant-mycorrhizal nutrient exchange, MAMP signaling, effector action and symbiotic signaling. Running time: 10:06, or 2:29 for recommended segment 1:57–4:26. Produced by UFZde, 2014.