If you can't stand the heat, get infected!

Are viral and fungal infections always a bad thing?

Maybe not if you're a plant.

In fact, if you're a plant trying to grow in the hot (65°; C) soils of Yellowstone National Park, you're going to need all the help you can get.

A new study by Márquez, et.al. (1) found that a type of grass (Dichanthelium lanuginosum) is able to grow in the hot soils of Yellowstone National Park because it gets help from some friends. A fungal friend. And that fungal friend is infected with a virus.

If you're not used to thinking in degrees centigrade, it's hard to grasp immediately, just how hot 65°; C is. For those of us in the U.S., it corresponds to 149°; Fahrenheit. Hot enough to melt short fragments of DNA and hot enough to kill many bacteria. In fact, one method for pasteurizing milk kills most bacteria by heating it at 62.9°; C for 30 minutes.

So how do plants manage to stand the heat?

If we're going to adapt to global warming and grow food under new climate conditions, this is something we might need to know.

The experiments
Márquez et. al.(1) knew that these plants were infected with a fungus called Curvularia protubera. In studying the fungus, they realized that fungus was itself infected, with a virus, composed of double-stranded RNA. Since viruses can impact the way a fungus behaves, they decided to see if the virus had anything to do with the ability of these plants to grow in high temperatures.

They grew some of the fungus on petri plates and isolated a strain that had lost the virus (Virus Free). Then they reinfected the viral-free strain with virus. Last, they tested the abilities of different plants, infected and uninfected, to grow in hot conditions.

In the experiment below, they looked at tomato plants. Some were infected with viral-infected fungus (Wt and An), one wasn't infected with fungus (or virus), and one was infected with a viral-free fungus (VF).

This graph shows the numbers of plants that were dead (black) or alive (white) after being exposed to heat (65°; C) for 10 hours a day.

To be healthy at a hot temperatures, requires both the virus and the fungus, but how the virus and the fungus help the plants tolerate heat is unknown.

Reference:
1. Márquez, L., et. al. 2007 A Virus in a Fungus in a Plant: Three-Way Symbiosis Required for Thermal Tolerance Science 26: 513-515.