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Metabolic Studies and Bioengineering of Plant Trichomes Towards Enhancing Pest/Disease Resistance and Facilitating Molecular Farming
G. J. Wagner
Department of Plant and Soil Sciences
The work described in this project is directly related to world-wide efforts towards "molecular farming" to exploit plants for sustainable production of non-traditional, commercially-valuable products, i.e., non-food or fiber products. The success in these efforts will depend on acquiring a better fundamental understanding of the metabolism and metabolic regulation underlying plant surface secretion processes, coupled with direct efforts to apply available tools to manipulate these systems towards a useful purpose.
Our work is focused on exploitation of plant trichomes to enhance natural-product-based pest/disease resistance and develop possibilities for molecular farming of trichome secretions that might be used to protect other plants (e.g., food crops, ornamentals) against damage from pests and disease, or as commercial chemical feed-stocks.
A new and recent focus stems from our discovery of antifungal proteins we have called "phylloplanins" that are also produced on aerial surfaces of certain plants. There is a growing need for novel fungicides, particularly natural product based compounds, to augment and replace currently used, chemically-synthesized products whose marketability is under challenge because of environmental concerns.
2010 Project Description
We have continued studies of phylloplanins and have shown for a second year of field trials that T-phylloplanin is effective against grey leaf spot, brown patch and dollar spot after spraying perennial rye and bentgrass with aqueous solutions containing T-phylloplanin (as T-LWW). Thus results of the previous field trial (2009) constitute 2 consecutive years of positive efficacy results. Studies relating to the mechanism of action of phylloplanins were continued to show that T-phylloplanin causes proton leakage from artificial phospholipid vesicles as well as tonoplast vesicles derived from tobacco roots. These studies included the monitoring of proton leakage induced by the known pore forming peptides nicin and polymixinB. Thus T-phylloplanin was shown to behave as a pore former to cause ion leakage in artificial membranes, consistent with a pore forming mechanism of action.
A blue mold sensitive tobacco when transformed with a T-phylloplanin containing gene construct conferred blue mold resistance to Peronospora tabacina. This trait was shown to be retained in seed from third generation (T2)plants. In collaborative studies T- and S-phylloplanins were found to inhibit a specific fungal disease of honey bees. A specific diterpene product of tobacco trichome exudate was shown to confer resistance to black shank and pithium diseases of tobacco .
Results of this period substantiate results found earlier that describe trichome-derived tobacco and sunflower phylloplanins as broad spectrum fungicides that may serve as topical anti-fungals against a variety of fungal and oomycete pathogens. They also indicate that tobacco plants engineered to produce elevated levels of T-phylloplanin fusion proteins are protected against blue mold disease.
Regarding the mechanism of action of T- and S-phylloplanins, experiments extended to artificial phospholipid vesicles confirm that these antifungal agents cause pore formation in membranes resulting in ion leakage and inhibition of pathogenicity. Field studies in this period substantiate results obtained in the previous year and thus we have two years of data showing efficacy in the field. These field trials suggest that phylloplanins can be useful in IPM management of golf courses, athletic fields, residential and business lawns as well as on sod farms to reduce reliance on chemically synthesized fungicides.
Results of our collaborative work on honey bee protection from fungal disease is consistent with the potential usefulness of phylloplanins in this important agricultural industry.
Shepherd, R.W., Wagner, G. J. 2010. Fungi and the leaf surface: the phylloplane. In Plant Fungal Interactions, D. Southworth, ed (Wiley-Blackwell, Ames, IA), in press.