An ecologic m￩nage ￠ trois

ﾩ 2006 AAAS

A virus in a fungus in a plant: This three-way symbiosis was discovered in a tropical panic grass Dichanthelium lanuginosum. Marilyn J. Roossnick of the Samuel Roberts Noble Foundation in Ardmore, Okla., and collaborators were examining an endophytic fungus, Curvularia protuberata, which inhabits the roots of the grass, allowing it to grow in the high-temperature soils of Yellowstone National Park. They isolated a dsRNA virus in the fungus necessary to maintain the high-temperature tolerance. ¹ Joe Heitman, of Duke University Medical Center calls the paper "fascinating."

In Faculty of 1000, Heitman writes: "Earlier studies have revealed that symbiosis between a fungus and a plant enabled the two to survive growth at temperature extremes as high as 65ﾰC. This study reveals a third partner in this m￩nage ￠ trois symbiosis, a fungal virus dubbed the Curvularia thermal tolerance virus (CThTV), [which] is necessary for the fungus to confer thermal tolerance.

"Isolates cured of the virus by a freeze/thaw cycle establish symbiosis but do not protect from temperature extremes, whereas reinfection by hyphal anastomosis restores the ability of the symbiont to protect both itself and the plant partner. Remarkably, growth of the fungus on a nonhost plant, tomato, conferred increased heat tolerance. These findings have profound implications for our appreciation of the importance of symbiotic relationships, and likely have practical implications for agriculture."