Team:British Columbia/Background

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Abstract

From left to right: a view from Mount Fraser of dying pine trees turning red, a pine beetle, the effects of the bluestain fungus on a pine tree.

In nature, monoterpenes are synthesized and secreted by trees as a defense against invading beetles and fungi. In one case, the bluestain fungus and mountain pine beetle are in a symbiotic relationship where the fungus deactivates toxic terpenoids and enables the survival of the beetle, which in turn facilitates the spread of the fungus from tree to tree.

From left to right: terpenoids are commonly used in pharmaceutical, flavors & fragrances and biofuel industries, an example of yeast's industrial utility: beer-brewing.

Meanwhile, from an industrial point of view, various monoterpenes are involved in the production of pharmaceuticals, flavours/fragrances and biofuels.

The 2011 UBC iGEM team aims to address both aspects by engineering yeast that produce monoterpenes with high yield at low cost, which may also help in the identification of anti-fungal monoterpenes. To do this, we will introduce genes that gear yeast metabolism toward optimal monoterpene production. We envision that further studies arising from this project may be utilized to find solutions to the pine beetle epidemic.

Background

The mountain pine beetle (MPB) outbreak in British Columbia (B.C), Canada, is the largest and most widespread of its kind in North America, and has reached an unprecedented level since 1995. To date, this epidemic has killed millions of acres of lodgepole pine trees, endangering the forest health, which hosts a wide range of ecosystems, and threatening the economic, social, and cultural stability of our beautiful province. Currently, the area of most intensive outbreak is situated in the interior of British Columbia and is predicted to spread outwards to the rest of the province and to the bordering province of Alberta. And by 2013, according to the B.C Ministry of Forests and Range, mortality of all merchantable pine trees is projected to be as high as 80 percent.

This mountain pine beetle, native to B.C, affects pine trees by laying their eggs under the bark of the tree. However, the culprit responsible is not merely the beetle itself, rather the blue stain fungus (Grosmannia clavigera) which lives in symbiosis with the MPB, also plays a key role in the infestation. By laying their eggs, the beetles simultaneously introduce the blue stain fungus into the sapwood, which helps prevent the tree’s natural defences, a resin flow, from repelling and killing attacking beetles. Due to this action, both the beetle and fungus are able to overcome the tree’s defences and colonize the insides of the tree through this dual action. Through this, the fungus cuts off water and nutrient transport within the tree, while beetle larvae feed off the tree. Within a year, the pine tree will die from lack of water and nutrient transport, as its needles will turn red. Mature MPB will leave the dying tree and move on to the next host tree. And in the upcoming years following the attack, the tree will turn gray with very little foliage left on the tree. Throughout this entire process, most wood is unsalvageable, due to the bluish-black stain left behind on the wood by the fungi and consequently the degrading value of the wood. With vast amount of pines being killed, this has also become a fire hazard for B.C forest. The mountain pine beetle has always been present in nature and has never been a problem until the beginning of this century. Recent climate changes has resulted in warmer than usual winters which has permitted the survival of these beetles during the winter. Therefore, its population has grown substantially over the past 15 years. The government of Canada and B.C.’s Ministry of Forestry has already committed over $956 million dollars to mitigate the spread of the MPB to more pine trees in B.C. However, no permanent solution has been found so far.

Despite not finding a solution to the MPB infestation, a lot of research and time has already been invested in studying the genetics and molecular systems of the three players involved: the pine tree, the mountain pine beetle, and the blue stain fungus. Interestingly, it was noted that not all pine trees in outbreak area are infested with the MPB. This begs the question: why do not all pine trees get attacked or infested by the pine beetle? Researchers have explored this question and in genomic studies comparing attacked pines to those left unharmed, a greater expression of genes related to monoterpene production, were observed in unharmed trees relative to the genetic expression in attacked trees. In nature, these monoterpenes (molecular formula C10H16), a class within the family of terpeniods, are synthesized and secreted by trees as a defence mechanism against insect and fungi infestation within the tree. Despite this finding, the bluestain fungus has also adapted itself very well to the tree’s natural defenses by metabolizing these terpenoids and removing it from its system; and hence is able to survive under these toxic conditions. However, researchers have postulated that the blue stain fungus is able to evade these conditions only by attacking stressed trees, where levels of monoterpenes produced are less than normal and thus more susceptible to attacks.