Fungal and Bacterial Resistance in Transgenic Trees

Abstract

In our global economy, the movement of living materials around the world is having a homogenizing effect on previously isolated ecosystems. One of the consequences of this movement is the introduction of many exotic species including plant pathogens. Pathogens that have co-evolved with their host usually reach a balance where both organisms can survive within an ecosystem. But when these same pathogens are introduced to similar species in a different area of the world, the consequences can be devastating. Tree diseases such as white pine blister rust, chestnut blight, beech scale complex, Dutchelm disease, butternut canker, and dogwood anthracnose, to name just a few examples, have caused significant losses of trees in North American forests and urban settings. Although regulatory safeguards on trade are in place, diseases such as the newly discovered sudden oak death in the western United States, sometimes get through. It is likely that new introductions of diseases and pests will continue into the foreseeable future. In addition, high intensity forest plantations are being developed to supply the world’s need for wood products and fiber, which will likely bring new challenges to disease control. Therefore, the development of trees with enhanced resistance to pathogens is necessary to maintain healthy natural forests as well as agroforestry plantations. A transgenic approach for enhancing pathogen resistance in trees is a promising way to restore trees to the forest that were previously devastated by exotic pathogens as well as to prevent such problems in the future. Significant progress to enhance pathogen resistance through genetic engineering is being made in crop plants. The general approaches include the expression of a variety of antimicrobial proteins or organic molecules, enhancement of the hypersensitive response (HR), and the enhancement of systemic acquired resistance (SAR) (Grover and Gowthaman 2003). Some of the approaches used in crop plants may be applicable to trees, but there are several unique properties of trees to consider when mapping one’s disease enhancing approach. These include the long lifespan of a tree, that trees are present through all seasons and might have varying susceptibility among the seasons, and that trees have important associations with symbiotic microorganisms such as mycorrhizae. 11 Fungal and Bacterial Resistance in Transgenic Trees