Monday, January 4, 2016

A piping hot plant-fungus-virus three-way

The Star Wars prequels, while fairly awful, managed to include a little bit of fictional biology. It turns out being sensitive to the Force, the mystical energy field that lets you confuse stormtroopers and toss debris at newly-minted amputees, requires having a whole lot of midi-chlorians in your cells. Midi-chlorians are clearly a bastardization of mitochondria, the squiggly energy-generating jelly beans (er, organelles) found within cells of all organisms except bacteria and archaea.

Just as midi-chlorians live inside cells and give fictional characters the ability to access the Force, real-world microbes can take up residence in the cells of larger organisms and gift them with cool abilities. For example, most plants are inhabited by fungi that help them deal with environmental stresses (e.g. drought, being eaten by herbivores) in return for food and shelter. These endophytes ('within plants') usually don't appreciably harm the plant, growing their filaments in the spaces between cells to minimize their impact.

Dichanthelium lanuginosum (commonly known as panic grass, which sounds like a really terrible variety of weed) is a species of grass found in Yellowstone and other geothermal regions of the western USA. Unlike the vast majority of plants, it's able to grow in warm soils that can reach up to 65°C on occasion.

Dichanthelium lanuginosum hanging out at the edge of a hot spring (Source)

The ability of this grass to tolerate high temperatures is due to its roots and leaves being colonized by a fungus called Curvularia protuberata (image of its filaments and candy corn-like spores). On their own, neither organism can withstand temperatures above 38°C, but together they become a potent heat-tolerating force.

Making things even more interesting, the fungus is itself host to a virus (a double-stranded RNA virus, to be precise). If you cure the fungus of the virus, fungus-colonized plants are unable to survive high temperatures. For this reason, it's been named the Curvularia thermal tolerance virus. It's possible to introduce the virus-infected fungus into other plants such as tomatoes, causing them to become heat tolerant!

When temperatures rise, the virus causes the fungus to produce greater amounts of particular enzymes involved in making and breaking down molecules known to help plants survive water loss (e.g. trehalose). This suggests these molecules have an additional role in enabling the grass to deal with the effects of high temperatures.


References

Márquez LM, Redman RS, Rodriguez RJ, Roossinck MJ. 2007. A virus in a fungus in a plant: Three-way symbiosis required for thermal tolerance. Science 315(5811):513-515.

Morsy MR, Oswald J, He J, Tang Y, Roossinck MJ. 2010. Teasing apart a three-way symbiosis: Transcriptome analyses of Curvularia protuberata in response to viral infection and heat stress. Biochemical and Biophysical Research Communications 401(2):225-230.

http://jgi.doe.gov/why-sequence-curvularia-protuberata/

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