Location: Natural Products Utilization Research
2017 Annual Report
Objectives
The overall goal of this project is to discover and develop natural product-based weed management solutions. The research is divided into discovery and development of biochemicial bioherbicides and creation of crops that are resistant to weeds by transgenically imparting or improving plant/plant allelopathy. This research should provide new avenues for the development of affordable and effective, yet sustainable, weed control strategies.
Objective 1: Discover and develop natural product-based bioherbicides that provide environmentally safe and toxicologically benign tools for weed management, with novel modes of action, to address current problems associated with herbicide resistant weeds.
Subobjective 1.1: Discover new and existing natural products for potential use as herbicides and bioherbicides.
Subobjective 1.2: Discovery of the mechanisms of action for newly discovered phytotoxins using chemical structure clues and physiological evaluations.
Subobjective 1.3: Develop natural products as new weed management tools.
Objective 2: Develop plant-incorporated bioherbicide technologies for weed management based on known or newly discovered allelochemicals.
Subobjective 2.1: Complete the characterization of the gene products of putative genes for enzymes of the sorgoleone biosynthetic pathway.
Subobjective 2.2: The use of sorghum transformants possessing altered sorgoleone levels to investigate the ecophysiological role of sorgoleone.
Subobjective 2.3: Identification of plant promoters to facilitate root hair-specific metabolic engineering of sorgoleone biosynthesis.
Subobjective 2.4: Engineering de novo sorgoleone biosynthesis in non-producing host plants.
Approach
Bioassay-directed isolation of phytotoxin will be followed by their evaluation of their potential as bioherbicides and determination of their modes of action. Genes of the sorgoleone synthesis pathway with root hair-specific promoters will be inserted into plants with the intent to impart or improve allelopathic capacity for enhanced weed management.
Progress Report
Objective 1. Pyrichalasin H was identified as the phytotoxic compound from the culture broth of the fungus Pyricularia grisea that was isolated from infected Brachiaria (B.) eruciformis (signal grass), a common weed in the state of Mississippi. Brachiaria eruciformis commonly known as Signal grass is a common weed in lawns and turfs in the state of Mississippi. From infected leaves of B. eruciformis showing necrosis a fungus was isolated and identified as Pyricularia (P.) grisea. P. grisea, Magnaporthe (M.) gisea and P. oryzae are closely related fungi that are responsible for crop losses in rice and cereals worldwide. P. grisea was grown in culture broth. The ethyl acetate extract of the culture broth was found to be phytotoxic. The phytotoxic constituent, isolated by bioassay guided isolation, was identified as pyrichalasin H. We have also shown for the first time that pyrichalasin H has antifungal activity against Colletotrichum species. This study provides not only further evidence that plant pathogenic fungi are good sources of herbicidal compounds but also chemical basis for the necrosis in infected leaves.
A phytotoxic isochromene analog was identified from the culture broth of a fungus determined to be a member of the Phoma genus that was isolated from infected leaf of Malabar spinach (Basella alba), a popular green leafy vegetable native to tropical Asia. The compound was found to be phytotoxic.
Two phytotoxic compounds (tyrosol and a compound having an isocoumarin core structure) were identified from the Diaporthe eres-infected leaf of Hedera helix (English Ivy) exhibiting necrosis. Isocoumarin analogs were synthesized, and two of the analogs were two- to three-fold more phytotoxic than the naturally occurring compound in a Lemna paucicostata growth bioassay.
About 100 semisynthetic compounds from a visiting scientist were bioassayed, and several were found to have good herbicidal activity and one has a novel mode of action.
Analysis of RNA sequence data from treatment of Arabidopsis thaliana with the allelochemical chalcone found a massive effect on the genes for enzyme of the phenylpropanoid pathway and tyrosine metabolism.
Bioassay-guided isolation of phytotoxins from Artemisia arborescens found the two lignans, sesamin and ashantin, to account for most of the phytotoxicity.
Other materials from several collaborators were evaluated for phytotoxicity. Details cannot be provided here because of confidentiality agreements.
Objective 2. The characterization of transgenic sorghum plants expressing hairpin RNA (hpRNA) for repression of CYP71AM1 (RNA interference studies) was completed. Suppression of the expression of CYP71AM1 significantly reduced the production of sorgoleone.
Preparation of the multi-gene constructs for co-expression of sorgoleone biosynthetic enzymes driven by sorghum root hair promoters is completed.
Accomplishments
1. Phytotoxic compounds isolated from a rare plant in Brazil. Vellozia (V.) gigantean is a rare, ancient, and endemic neotropical plant present in the Brazilian Rupestrian grasslands. The dichloromethane extract of the adventitious roots of V. gigantea was phytotoxic against Lactuca sativa, Agrostis stolonifera, and Lemna paucicostata. Phytotoxicity assay-directed fractionation of the extract revealed one new isopimaradiene compound and three new cleistanthane diterpenoids. The new isopimaradiene compound was especially phytotoxic with activity comparable to those of the commercial herbicides clomazone, s-ethyl dipropylthiocarbamate (EPTC), and naptalam. With this study, ARS researchers in Oxford, Mississippi, show that ancient and unique plants, like the endangered narrowly endemic neotropical species V. gigantea present in the Rupestrian grasslands, should also be protected because they can be sources of new bioactive compounds.
2. Visualization of sorgoleone spatial distribution using matrix assisted laser desorption/ionazation-mass spectrometric imaging (MALDI-MSI) on whole sorghum root systems. Prior work performed by our research unit as well as other laboratories has conclusively demonstrated that biosynthesis of the natural herbicide sorgoleone occurs primarily or exclusively within root hair cells of sorghum plants. There is limited information however concerning the fate of this compound once it is extruded from these cells. For this reason ARS researchers in Oxford, Mississippi, investigated the use of an emerging analytical technique in plants referred to as mass spectrometry imaging (MSI), an adaptation of mass spectrometry which facilitates direct visualization of the spatial distribution of chemical compounds on tissue sample surfaces. Working in collaboration with Iowa State University, we completed an imaging study using matrix-assisted laser desorption ionization MALDI-MSI on 10-day-old sorghum seedlings. These studies demonstrated that sorgoleone accumulation is not localized to the root hair zone, but rather appears to form a continuous layer coating the entire root system of young seedlings. This would be consistent with the notion that this compound could function as a type of chemical barrier, serving as a defensive interface between the root system and surrounding soil environment.
Review Publications
Carvalho, L.B., Duke, S.O., Messa, J.R., Regina Da Costa, F., Bianco, S. 2016. Plant growth responses of apple and pear trees to doses of glyphosate. Planta Daninha. 34(4):815-822.
Travaini, M.L., Sosa, G.M., Ceccarelli, E.A., Walter, H., Cantrell, C.L., Carrillo, N.J., Dayan, F.E., Meepagala, K.M., Duke, S.O. 2016. Khellin and visnagin, furanochromones from Amni visnaga (L.) Lam., as potential bioherbicides. Journal of Agricultural and Food Chemistry. 64:9475-9487.
Duke, S.O., Rimando, A.M., Reddy, K.N., Cizdziel, J.V., Bellaloui, N., Shaw, D.R., Williams, M., Maul, J.E. 2017. Lack of transgene and glyphosate effects on yield, and mineral and amino acid content of glyphosate-resistant soybean. Pest Management Science. 74:1166-1173. https://doi.10.1002/ps.4625.
Moreas, R.M, A.L. Cerdiera, S.O. Duke, F.E. Dayan, C.L. Cantrell, and S.C.N. Queiroz. 2016. Pesticidas Naturais Derivdos de Plantas: Descoberta et Usos (Natural Pesticides Derived from Plants: Discovery and Uses). In: Halfeld-Vieira, B.A, Marinho-Prado, J.S., Nechet, K.L., Morandi, M.A.B., Bettiol, W., editors. Defensivos Agrícolas Naturais: Uso e Perspectivas (Natural Agricultural Defenses: Use and Perspectives). Jaguariúa, Brazil: Emprapa Meio Ambiente. p. 505-541.
Maroli, A.S., Nandula, V.K., Duke, S.O., Tharayil, N. 2016. Stable isotope resolved metabolomics reveals the role of anabolic and catabolic processes in glyphosate-induced amino acid accumulation in Amaranthus palmeri biotypes. Journal of Agricultural and Food Chemistry. 64:7040-7048.
Nascentes, R.F., Carbonari, C., Simoes, P.S., Brunelli, M.C., Velini, E.D., Duke, S.O. 2017. Low doses of glyphosate enhance growth, CO2 assimilation, stomatal conductance and transpiration in sugarcane and eucalyptus. Pest Management Science. doi:10.1002/ps.4606.
Duke, S.O. 2012. Why are there no new herbicide modes of action in recent years. Pest Management Science. 68:505-512.
Bajsa, J.N., Pan, Z., Duke, S.O. 2011. Serine/threonine protein phosphatases: multi-purpose enzymes in control of defense mechanisms. Plant Signaling and Behavior. 6(12):1921-1925.
Dayan, F.E., Owens, D.K., Duke, S.O. 2012. Rationale for a natural products approach to herbicide discovery. Pest Management Science. 68:519-528.
Bajsa, J.N., Pan, Z., Dayan, F.E., Owens, D.K., Duke, S.O. 2012. Validation of serine-threonine protein phosphatase as the herbicide target site of endothall. Journal of Pesticide Biochemistry and Physiology. 102(2):38-44.
Chen, Y., Li, J., Li, S., Zhao, J., Bernier, U.R., Becnel, J.J., Agramonte, N.M., Duke, S.O., Cantrell, C.L., Wedge, D.E. 2016. Identification and characterization of biopesticides from Acorus Tatarinowii and A. Calamus. American Chemical Society Symposium Series. 1218:121-143.
Wu, X., Yu, Y., Liang, G., Baerson, S.R., Pan, Z., Song, Y., Ding, C., Wu, W., Niu, J., Zeng, R. 2017. Interactions between nitrogen and silicon in rice and their effects on resistance towards the brown planthopper Nilaparvata lugens. Frontiers in Plant Science. doi:10.3389/fpls.2017.00028.
Ye, M., Song, Y., Baerson, S.R., Long, J., Pan, Z., Lin, W., Zeng, R. 2017. Ratoon rice generated from primed parent plants exhibit enhanced herbivore resistance. Plant, Cell & Environment. 40:779-789. doi:10.1111/poe.12897.
Duke, S.O. 2017. The history and current status of glyphosate. Pest Management Science. 74:1027-1034. doi:10.1002/ps.4652.
La Hovary, C., Baerson, S.R., Williamson, J.D., Danehower, D.A., Ma, G., Pan, Z., Mask, M.M., Burton, J.D. 2016. Phytotoxicity and benzoxazinone concentration in field grown cereal rye (Secale cereale L.). International Journal of Agronomy. 2016:1-11. doi:10.1155/2016/6463826.
Duke, S.O., Heap, I. 2017. Evolution of weed resistance to herbicides: What have we learned after 70 years? In: Jugulam, M., editor. Biology, Physiology and Molecular Biology of Weeds. Boca Raton, FL:CRC Press. p. 63-86.
Belz, R.G., Duke, S.O. 2017. Herbicide-mediated hormesis. American Chemical Society Symposium Series. 1249:135-148. 10.1021/bk-2017-1249.ch001.
Duke, S.O. 2017. Pesticide Dose - A Parameter with Many Implications. American Chemical Society Symposium Series. 1249:1-13. 10.1021/bk-2017-1249/ch001.
Ferreira, M.C., Cantrell, C.L., Duke, S.O., Ali, A., Rosa, L.H. 2017. New phytotoxic diterpenoids from Vellozia gigantea (Velloziaceae), an endemic neotropical plant living in the endangered Brazilian biome Rupestrian grasslands. Molecules. 22:175. doi:10.339/molecules22010175.
Stavropoulou, M.I., Angelis, A., Aligiannis, N., Kalpoutzakis, E., Mitakou, S., Duke, S.O., Fokialakis, N. 2017. Phytotoxic triterpene saponis from Bellis longifolia, an endemic plant of Crete. Phytochemistry. 144:71-77. doi:10.1016/j.phytochem.2017.08.019.
