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United States Department of Agriculture

Agricultural Research Service

2010 Annual Report

1a.Objectives (from AD-416)
To discover phytotoxins and allelochemicals for use in pest management and to provide the fundamental information on mode of action, structure-activity relationships, natural resistance mechanisms, and biosynthesis of natural phytotoxins that will be required for development medicinal/nutraceutical crops. To discover, characterize, manipulate and utilize genes involved in the production of natural products and in chemical defense and resistance mechanisms against allelochemicals and environmental phytotoxins.

1b.Approach (from AD-416)
Conduct bioassays in collaboration with research chemists during bioassay-directed isolation of new phytotoxins. Molecular sites of action will be determined with genomic and biochemical approaches. Biosynthetic pathways of toxins from plants will be investigated. Genes controlling synthesis of useful plant secondary products and plant defenses to phytotoxins will be identified, cloned, and manipulated.

3.Progress Report
Triketone-rich manuka oil was found to be a potent herbicide. It inhibits the enzyme p-hydroxyphenylpyruvate dioxygenase and can be applied as either pre or post-emergence spray. It is taken up through the leaves or roots and is translocated to other parts of the plant. Application of this compound on soils causes bleaching of the foliage of emerging plants. Pterostilbene derivatives were found to be phytotoxic which has been documented in the J. Agric. Food Chem. (Mizuno, C.S., A.M. Rimando, and S.O. Duke. Phytotoxic acitvity of quinone and resorcinolic lipid derivatives. 58:4353-4355) and listed on project 6408-41000-007-00D. Sorgoleone exudes from the tip of sorghum root hairs and is released into the soil, its persistence in soil is an important factor related to its allelopathic potential. Therefore, we determined the rate of mineralization of sorgoleone in soils that were exposed to sorghum roots in the past and in soils on which sorghum had never been grown. The methoxy group of sorgoleone was the most rapidly mineralized portion of the molecule, whereas the remaining molecule was slower to mineralize. Cytochrome P450 enzymes are proposed to be involved in sorgoleone biosynthesis. Four cDNA sequences encoding putative P450s were isolated from Sorghum root-hair cells. Constructs for characterization of these encoded enzyme activities were designed and made. The cloned cDNAs were expressed in a yeast expression system. Active forms of the enzymes were obtained by heterologous expression, and characterization of substrate specificities is in progress. Pterostilbene, chemically related to resveratrol, possesses antimicrobial activity and likely plays a defense role in plants. Pterostilbene has also generated interest as a nutraceutical, due to its potential role in promoting cardiovascular health, inhibiting tumor formation, and increasing cell longevity. We previously reported the development of a transgenic approach for the production of pterostilbene using the peanut STS3 sequence in conjunction with sorghum OMT3. Greenhouse studies were performed to examine the effects of constitutive pterostilbene overproduction on vegetative and reproductive development using multiple independent STS3/OMT3 transformed tobacco and A. thaliana events compared with controls. Constitutive STS3/OMT3 co-expression was not found to be associated with major effects on vegetative or reproductive development in either species, however, some reduction in floral pigmentation was observed in pterostilbene-producing tobacco transformants. Plant phenolic lipids can accumulate in plants as conjugates, thus the sequestration of sorgoleone precursors in this manner could account for the ability of Sorghum spp. members to synthesize large quantities of this compound without autotoxicity. A gene that may encode an enzyme involved in sorgoleone conjugation was identified. In silico expression analyses revealed this sequence to be moderately-to highly-abundant in root hair cells, where sorgoleone is produced.

1. Transgenic Manipulation of Sorgoleone Production in Sorghum. Sorghum plants produce a compound referred to as sorgoleone that could have beneficial properties for fighting weeds. ARS researchers at the Natural Products Utilization Research Unit, Oxford, MS, have uncovered critical genes required for the synthesis of this compound, and are manipulating its levels in sorghum plants by affecting the expression of one of these genes. Such manipulation could be very useful in improving the weed-fighting capacity of sorghum by increasing sorgoleone production. Conversely, knocking out sorgoleone production could reduce problems encountered by farmers planting other sensitive crop species in the same field immediately following a sorghum crop. Sorgleone may also play a role in cueing certain parasitic weeds in Africa to infect sorghum crops, and manipulation of sorgoleone levels in transgenic plants could potentially be useful for addressing this problem as well. The Grodzinsky Award, which recognizes the most outstanding publication of the previous three years from the International Allelopathy Society, was received for part of this research.

Review Publications
Herath, H., Herath, W., Carvalho, P., Khan, S.I., Tekwani, B., Duke, S.O., Tomaso-Peterson, M., Nanayakkara, N. 2009. Biologically Active Tetranorditerpenoids from Fungus Sclerotinia homoeocarpa Causal Agent of Dollar Spot in Turfgrass. Journal of Natural Products. 72:2091-2097.

Matallo, M.B., Almeida, S., Cerdeira, A.L., Franco, D.A., Garcia Blanco, F.M., Menezes, P., Luchini, L.C., Moura, M., Duke, S.O. 2009. Microwave-Assisted Solvent Extraction and Analysis of Shikimic Acid from Plant Tissues. Planta Daninha. 27:987-994.

Dayan, F.E., Duke, S.O. 2010. Protoporphyrinogen Oxidase-Inhibiting Herbicides. In: Hayes's Handbook of Pesticide Toxicology. R. Krieger, J. Doull, E. Hodgson, H. Maibach, L. Reiter, L. Ritter, J. Ross, W.J. Slikker and J. van Hemmen (Eds.), John Wiley and Sons, New York, NY. Vol. 2, PP 1731-1751.

Duke, S.O., Cerdeira, A.L. 2010. Transgenic Crops for Herbicide Resistance. Book Chapter. In: Transgenic Crop Plants, Vol. 2: Utilization and Biosafety. C. Kole, C.H., Michler, A.G. Abbott and T.C. Hall, Eds., Springer-Verlag, Berlin/Heidelburg, Germany. PP. 133-166.

Cerdeira, A.L., Duke, S.O. 2010. Effects of Glyphosate-resistant Crop Cultivation on Soil and Water Quality. GM Crops. 1(1):16-24.

Duke, S.O., Powles, S.B. 2009. Glyphosate-Resistant Crops and Weeds: Now and in the Future. Agbioforum. 12(3&4):346-357.

Duke, S.O. 2010. Allelopathy: Current Status of Research and the Future of the Discipline: A Commentary. Allelopathy Journal. 25(1):17-30.

Alsaadawi, I., Dayan, F.E. 2009. Potentials and Prospects of Sorghum Allelopathy in Agroecosystems. Allelopathy Journal. 24(2):255-270.

Cerdeira, A.L., Duke, S.O., Gazziero, D., Matallo, M.B., Bolonhesi, D. 2009. Transgenic Herbicide-resistant Crops and Environmental Impacts (Plantas Transgenica Resistentes a Herbicidas e Interacoes com o Meio Ambiente) in: Culturas Transgenicas: um Abordagem de Beneficios e Riscos (Transgenic Crops: an Overview of Risks and Benefits), V.C. Pipolo, Ed., Universidade Estadual de Londrina. pp. 153-171.

Cook, D., Rimando, A.M., Clemente, T.E., Schroder, J., Dayan, F.E., Nanayakkara, D., Pan, Z., Noonan, B.P., Fishbein, M., Abe, I., Duke, S.O., Baerson, S.R. 2010. Alkylresorcinol Synthases Expressed in Sorghum Bicolor Root Hairs Play an Essential Role in the Biosynthesis of the Allelopathic Benzoquinone Sorgoleone. The Plant Cell. 22:867-887.

Dayan, F.E., Daga, P.R., Duke, S.O., Lee, R.M., Tranel, P.J., Doerksen, R.J. 2010. Biochemical and Structural Consequences of a Glycine Deletion in the a-8 Helix of Protoporphyrinogen Oxidase. Biochimica et Biophysica Acta. 1804:1548-1556.

Dayan, F.E., Rimando, A.M., Pan, Z., Baerson, S.R., Gimsing, A., Duke, S.O. 2010. Sorgoleone. Phytochemistry. 71:1032-1039.

Dayan, F.E., Trindade, M., Velini, E.D. 2009. Amicarbazone, A New Photosystem II Inhibitor. Weed Science. 57:579-583.

Duke, S.O., Baerson, S.R., Gressel, J. 2009. Genomics and Weeds: A Synthesis. In: Weedy and Invasive Plant Genomics, C.N. Stewart, ed., Blackwell Publishing, Singapore. pp. 221-247.

Matallo, M., Almeida, S., Cerdeira, A., Franco, D., Luchini, L., Moura, M., Duke, S.O. 2010. Shikimic Acid Monitoring by HPLC with Diode Array Detector in Citrus sinensis Orchard with Glyphosate. Arquivos do Instituto Biologico Journal of Animal, Plant Sanity and Environmental Protection. 77(2):355-358.

Techen, N., Arias De Ares, R.S., Glynn, N.C., Pan, Z., Khan, I.A., Scheffler, B.E. 2010. Optimized Construction of SSR-enriched Libraries. Molecular Ecology Resources. 10(3)508-515

Velini, E.D., Duke, S.O., Trindade, M.B., Meschede, D.K., Carbonari, C.A. 2009. Modo de acao do Glyphosate (Mode of Action of Glyphosate in Portuguese). In Glyphosate, E.D. Velini, D.K. Meschede, C.A. Carbonari, and M.L.B. Trindade, Eds., Fundaçã de Estudos e Pesquisas Agricoloas e Florestais. Botucato-SP, Brazil. pp. 113-133.

Duke, S.O., Cantrell, C.L., Meepagala, K.M., Wedge, D.E., Tabanca, N., Schrader, K. 2010. Natural toxins for use in pest management. Toxins. 2:1943-1962.

Dayan, F.E., Duke, S.O. 2010. Natural Products for Weed Management in Organic Farming in the USA. Outlooks on Pest Management. 21:156-160.

Last Modified: 6/2/2015
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