Hidden Heat Shield
Sweet grasses are true survivors: they settle in all climate zones, even dry steppes or savannahs are not safe from them. And if it becomes too inhospitable, look for suitable subtenants.
Over the millennia, plants have managed to penetrate almost every area of our planet. They inhabit extremely dry and very humid regions, get along with the most diverse soils and climate fluctuations. The heat, however, is still the biggest enemy of root bearers. But here, too, there are individual survivors.
An inconspicuous plant from the sweet grass family adapts particularly well to extreme temperatures. Dichanthelium lanuginosum even settles on the edges of geysers and hot springs in Yellowstone National Park - with soil temperatures of up to 50 degrees Celsius. Where every single root fiber would have withered away long ago in other plants, the grass is in the best of he alth.
The reason for this extreme heat resistance is buried deep in the hot earth. Because the sweet grass hides a fungus in its root system, for which it would be a little too hot outside the plant body itself. A US research group headed by Regina Redman from the University of Washington in Seattle discovered a few years ago that the team can only cope with the high temperatures if they work together. But in order to protect its host, the fungus Curvularia protuberata also needs a little support, as scientists led by Marilyn Roosinck from the Samuel Roberts Noble Foundation found out on closer inspection. He, too, keeps a permanent guest – in the form of a viral infection.
A genetic analysis of the mushroom mycelium revealed the unusual collaboration. While examining the genome, the researchers came across double-stranded RNA molecules. These gene building blocks are not normally found in fungi, but they are in some plant viruses. Further tests confirmed the suspicion: the fungus was infected with a virus. "Most of these fungi are infected with viruses," says Marilyn Roossinck. Still, the researchers were alarmed: could the viral disease of the symbiotic fungus explain the grass's unusual heat resistance?
Not every virus is a carrier of disease. This is the story of a virus that makes its host he althier
(Marilyn Roossinck) To find out, the scientists froze some samples of the mushroom mycelium at minus eighty degrees and then grew them again in a Petri dish. The viruses were destroyed by the cold shock, so the new sample was virus-free. The scientists then transferred these fungal samples to some offshoots of the previously fungus-free sweet grass and compared the artificial community with the wild type. Lo and behold: the laboratory plants without the virus wilted miserably at high temperatures and died in a very short time, while the wild types easily survived two weeks at a soil temperature of 65 degrees Celsius.
However, when the virus-free fungi in the grass roots were reinfected, the plant's heat resistance also improved rapidly. Only in a pack of three does the community achieve the skills they need to survive. "Not every virus is a vector of disease," Roossinck concludes, "and this is the story of a virus that makes its host he althier." The unusual collaboration is apparently not limited to the grass: a tomato plant that the researchers planted with fungus and virus also showed improved heat resistance.
What exactly triggers the hardening of the plant has not yet been clarified with certainty. Harmful free radicals may play a role. These are less common in plants that have been exposed to great heat if they live symbiotically. However, the researchers found no difference in terms of free radicals in the lab-grown symbionts with or without the virus. The exact relationships between the three very different commune members remain in the dark for the time being. Perhaps in a few years, Redman's research group will provide another piece of the puzzle to solve the mystery.
