Describe the tri-partite symbiosis between tropical panic grasses, fungal endophytes, and viruses. Which microbial partner is more beneficial to the plant - the fungus or the virus?

Question

What will be an ideal response?

Answer 1

Plant vessels are colonized by endophytic microbes. Tall fescue is a grass grazed by cattle in the southeastern US. It is well-known for hosting foliar and stem endophytes. The fungus produces alkaloids that deter insect predators, pathogens, and root-feeding nematodes. Other kinds of endophytes protect plants from heat, salt, and drought. A plant-fungal symbiosis between grass and a fungus allows both organisms to grow at high soil temperatures (65oC) in Yellowstone National Park. When root zones are heated up to 65°C, non-symbiotic plants either become shriveled and chlorotic or simply die, whereas symbiotic plants tolerate and survive the heat regime. When grown separately, neither the fungus nor the plant alone is able to grow at temperatures above 38°C. However, the plant can only grow at high temperatures when it is infected with both the fungus (Curvularia protuberata) and it's viral symbiont (Curvularia thermal tolerance virus; CThTV). When plant roots are maintained at 65°C for 10 hours under greenhouse conditions, plants that are nonsymbiotic (NS) and symbiotic die. The wild-type plant inoculated with a virus-infected isolate of the endophytic fungus C. protuberata (Wt) and a hygromycin-resistant isolate of C. protuberata newly infected with the virus both persist under these conditions. However, when a plant is inoculated with a virus-free hygromycin-resistant isolate (VF) of C. protuberata, it is not able to withstand the heat.