Wednesday, February 15, 2012

Curvularia thermal tolerance virus (CThTV)

The satirist Jonathan Swift once wrote:
So, naturalists observe, a flea
Has smaller fleas that on him prey;
And these have smaller still to bite ’em;
And so proceed ad infinitum.[1]
Here, with Curvularia thermal tolerance virus (CThTV for short), we have a virus which infects a fungus which infects a plant. But what makes this virus interesting is how it affects both the fungus and, by extension, the plant.

As you can guess from the name, Curvularia thermal tolerance virus infects a fungus [2] called Curvularia. Curvularia protuberata, to be exact. Curvularia protuberata is symbiotic, rather than pathogenic. It infects a species of panic grass found in Yellowstone National Park, Dichanthelium lanuginosum. It has been known for a while that when grown in symbiosis, both the fungi and the grass are able to tolerate soil temperatures up to 65°C.[3] When grown separately, neither organism can tolerate such high temperatures. Within the last few years [4] it has been determined that it is actually the virus that makes this possible. If you cure the fungus of the virus and then infect the plant, they are unable to grow at high soil temperatures. Just for fun, the scientists who made this discovery tried infecting tomato (Solanum lycopersicon) plants with CThTV-infected Curvularia protuberata and had similar results. Once we understand how the virus does this, we may find a way to adapt it into a technology that lets us use unfavorable soils (i.e. too-hot soils) for agriculture.


[1] Swift, Jonathan. (1733) On Poetry: a Rhapsody. You can find it, and many other of Swifts' works here, at Project Gutenberg (scroll down). The mathematician Augustus De Morgan expanded on this theme:

"Great fleas have little fleas upon their backs to bite ’em,
"And little fleas have lesser fleas, and so ad infinitum.
"And the great fleas themselves, in turn, have greater fleas to go on;
"While these again have greater still, and greater still, and so on."
                             —De Morgan, Augustus. (1872) A Budget of Paradoxes, p. 377.

This eventually became a nursery rhyme, called The Syphonaptera.

[2] Another name for a virus that infects fungi is mycovirus.

[3] Stout, R. G.; Stout R. G., Summers M. L., Kerstetter T., McDermott T. R. (1997). "Heat- and acid-tolerance of a grass commonly found in geothermal areas within Yellowstone National Park". Plant Science 130 (1): 1–9.

[4] Márquez, Luis; Regina Redman, Russell Rodriguez, Marilyn J. Roossinck. (2007). "A Virus in a Fungus in a Plant: Three-Way Symbiosis Required for Thermal Tolerance". Science 315 (5811): 513–5.

Image attributions:

Dichanthelium lanuginosum is by the USGS (and is therefore public domain), available at or . 

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