Thompson Rivers University

Mistletoe’s hidden secret

  Posted on: December 10, 2013

From a story originally published December 17, 2012, by Diana Skoglund

While mistletoe is a happy symbol of this festive holiday season, few people likely know that the plant itself lives a life of underworld drama and espionage. Researchers at TRU have begun to unravel some of the mysteries connected to North American dwarf mistletoe’s fascinating life story.

Dr. Cynthia Ross Friedman, a TRU biologist, has built her career around understanding how mistletoe lives off of trees in Canada’s pine forests to become a successful parasite.

Through recent work with an undergraduate student (Lyssa Martin) and TRU Alumna, Dr. Lori Phillips, Ross Friedman has now shown that mistletoe has become adapted to defend itself against other kinds of parasites that would steal its hard-won riches.

No Christmas Story here, the modus operandi of mistletoe is straight from a mobster novel.

Close up view of female dwarf mistletoe

A close-up of female dwarf mistletoe, collected from lodgepole pine near Stake Lake, Kamloops, BC in August, 2010.

Mistletoe ‘hires’ protection—it harbours a fungus that lives among its cells. This hired gun guards its boss against invasion from free-living moulds (and other fungi) that would rob it of the fruits of its labours.

In tests, they found that the protective fungus, one akin to our own gut flora, could actually halt the growth of nasty mould fungi that would otherwise attack the mistletoe. This has serious implications:  knock out the hired gun, and the attacking mould might take over, providing a possible way to control mistletoe parasitism.

Although “good” fungi have been discovered in other plants, this is a first for dwarf mistletoe, and only the second time there has been any report of any fungus like this in any mistletoe.

Their findings, published in the December 2012 issue of the American Journal of Botany, could lead to further research identifying natural defences through which humans could protect themselves from fungal diseases.

Mistletoe spotting

Cynthia Ross Friedman (right) Lyssa Martin (middle) and Arvin Dwarka check pine tree branches in the Stake Lake area for the dwarf mistletoe parasite.

American Dwarf Mistletoe, a.k.a. Lodgepole Pine Dwarf Mistletoe

Though in the same family as the evergreen European mistletoe traditionally used to deck the halls (Viscum album), Ross Friedman explains our American dwarf mistletoe is Arceuthobium americanum , also known as lodgepole pine dwarf mistletoe. The sample in the first image above was collected by Ross Friedman’s team from lodgepole pines near Stake Lake in Kamloops.

“Most dwarf mistletoes are ‘dioecious’, meaning they have separate male and female plants,” says Ross Friedman. “The one being held is a female, and I would guess it was sampled mid-August.”

“It is a particularly neat shot, as it shows three generations of female flowers: young unfertilized flowers (the smallest scale-like nubs), fruits that are in their first summer of development (like bishop’s hats or “miters”), and fruits that are in their second summer of development (the larger, curved fruit).

“Young female flowers develop in late August, overwinter, and will be fertilized the following spring to form immature fruit that then enter their first summer of development. These immature fruit will go into another overwintering period, and then complete development over the second summer. At the end of that second summer, the seed is explosively-discharged from the mature fruit to find a new host pine. New flowers appear every year, hence the presence of all three generations in August.”

The flowering part of the plant shown here protrudes from the bark of the pine, with a root-like structure beneath that penetrates the bark to take water and nutrients from the tree.

UPDATE: Published research in February 2013 told of some interesting discoveries.

“We have seen molecular evidence—namely, the visible accumulation of a specific protein—indicating that the dwarf mistletoe might raise its temperature (i.e., “get a fever”) in order to explosively-discharge its seeds,” says Ross Friedman. “We are currently working towards obtaining direct evidence of this purported temperature increase. So far, the data support our ideas.”

Here’s how to find the research…

Ross Friedman, C.M., Ross, B. N., and Martens, G.D.  (2013).  An antibody against a conserved C-terminal consensus motif from plant alternative oxidase (AOX) isoforms 1 and 2 labels plastids in the explosive dwarf mistletoe (Arceuthobium americanum, Santalaceae) fruit exocarp.  Protoplasma. 250(1): 317-323.   DOI: 10.1007/s00709-012-0414-6

CBC Radio program Quirks and Quarks interviewed Ross Friedman about her discovery:

Quirks and Quarks Interview

Dr. Cynthia Ross Friedman,
TRU Professor Biological Sciences
Phone: 250-828-5424