First three way symbiotic relationship involving a virus.

TreeCo

Science News Online

Week of Jan. 27, 2007; Vol. 171, No. 4
Secret Agent: Hidden helper lets fungus save plants from heat

Susan Milius

The story of a fungus that keeps plants from withering in hot soil turns out to have been missing a character?the virus that makes it all work.

GOOD VIRUS. A tomato seedling (top) is more than twice as likely to take the heat if it harbors a fungus infected with a newly identified virus rather than an uninfected fungus (bottom). Seedlings spent 2 weeks in soil heated daily to 65?C.

The fungus Curvularia protuberata grows inside plant tissues without damaging them. In 2002, researchers working in Yellowstone National Park reported that grass colonized by the fungus thrived in soils that simmer at over 40?C (104?F) all summer.

A closer look now shows that the fungus alone doesn't protect plants from heat, says virologist Marilyn Roossinck of the Samuel Roberts Noble Foundation in Ardmore, Okla. The fungus itself has to be infected with a previously unknown agent, which she and her colleagues have named Curvularia thermal-tolerance virus, the group reports in the Jan. 26 Science.

Researchers haven't found many three-partner mutual-benefit societies, and this is the first plant-fungus collaboration known to have a virus as a third party, Roossinck says. She speculates that new ways to protect crops from heat might eventually result from understanding this threesome.

"I would hope that it changes people's thinking about viruses," Roossinck says. Scientists have primarily chosen to study viruses that cause disease, but she says that she suspects that most viruses don't have ill effects on their hosts. "There's a huge world out there that hasn't been looked at," she says.

Researchers discovered the original grass-fungus arrangement in a species of what's called panic grass, Dichanthelium lanuginosum.

While working on a different project in 2003, Roossinck looked through the Yellowstone Curvularia samples. She found signs of viral infection in the fungi in hot spot grasses but not in fungi from cooler places. Yellowstone soil can heat up to 50?C.

Roossinck and her colleagues isolated the virus and tested its powers in both the grass and tomato plants. One of the challenges that she faced was the failure of standard techniques to cure the fungus of its viral infection. However, when bringing fungal samples out of storage, Roossinck serendipitously discovered that freezing destroys the virus but not its host.

After Roossinck removed the virus by freezing the fungus, the latter no longer offered even limited protection to tomato plants. When she reinfected the fungus, its protective powers returned.

The new study "nicely demonstrates the complexity of plant-microbial interactions," says Stan Faeth of Arizona State University in Tempe, who studies grass and their live-in fungi.

The newly described three-way partnership reminds Nancy Moran of the aphids that she studies, which depend on resident bacteria for defense against parasites. Moran, who's at the University of Arizona in Tucson, showed that a virus in the bacteria provides the genes for toxins that could protect the host.

Live-in helpers "are a way for multicellular hosts, such as plants and animals, to acquire new ecological capabilities without actually incorporating foreign genes directly into their genomes," she says. "And viruses collectively have the greatest diversity of any genomes."

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Brother Colin

WOW. that is very fasinating stuff.

TreeCo

Thanks.

If mycorrhizae are found to be symbotic with viruses it would really get interesting. Notice in the article the virus was killed by freezing. I have read that soil temperature limits the range of some trees because of the percentage of die off of small roots over the winter. The tree must expend energy to regrow these roots in spring and the more that die.....the bigger the energy drain. It would be quite interesting if the virus involved in the symbiosis dies from the cold and therefore was part of the soil temperature growth limitations we see in trees.

I bet the people at PHC find this research interesting.

Eric Frei

In a place like Australia where 90% of the joint is hot desert it's good news and could possible mean more vegetation in harsher conditions.

Just have to spread the virus .... sounds like some sci-fi movie. Imagine the carry on trying to say it's OK.

__________________

Sean Freeman

Really great post TreeCo, one of my favourite pet subjects fungi and trees.

There really is masses of work being done in this field and new understandings are being gained almost weekly. Here's a bit of research from your side of the pond back in 97' I think from the Connecticut Exoerimental Agricultural Station they did and do really good work, here's the web address;

http://www.caes.state.ct.us/Default.htm

and the paper;

PP044.doc

The better we get at understanding that although the tree trunk and branches, and leaves look clean and smooth, its covered with fungal spore growth, bateria paramecium etc.. and on the inside its just as cluttered with fungal mycelia attempting to colonise wood tissue...the better we will become at assiting in the management of our trees whereever we might be.

SF

TreeCo

Thanks Boa.

That was an interesting read. I had not heard of such research.

From the article:

"Chestnut trees with blight cankers can be cured with mud packs applied to each canker, or protected with a biological control based on a virus that keeps the blight fungus from killing trees."

jim1nz

Very very interesting guys.

"when bringing fungal samples out of storage, Roossinck serendipitously discovered that freezing destroys the virus but not its host"

I find it quite evident that here in NZ, we have such a diverse climate throughout such a small area, virus and bacteria are able to thrive in warm climates especially but in areas with high climatic change diseases are unable to survive even though the host continues to thrive.