Dean E. Riechers

Research Interests

My research interests focus on understanding the biochemical and molecular basis for herbicide selectivity between crops and weeds. Specific research areas include characterization of the enzymes involved in herbicide metabolism (such as the glutathione S-transferases), mechanism of action of herbicide safeners in enhancing crop tolerance through increased herbicide detoxification, and mechanisms of herbicide resistance in problem weed species in the Midwest. My laboratory will utilize biochemical and molecular techniques to address these issues, including protein purification, immunoblotting, genomic and cDNA cloning, DNA and RNA hybridizations, and PCR and RT-PCR.

Research Program

Characterization of Glutathione S-Transferases (GSTs) in Triticum tauschii

We have cloned and sequenced three GST genes from Triticum tauschii, which is a wild progenitor of cultivated wheat, Triticum aestivum. We are utilizing T. tauschii as a model plant system to study the regulation of GST gene expression by herbicide safeners. Reasons for using T. tauschii as a model system are that it is diploid, contains the D genome found in cultivated wheat (ABD genomes), and also responds to safeners in a similar manner as cultivated wheat.

Herbicide safeners protect grass crops from herbicide injury by increasing the activity of herbicide detoxification enzymes, such as GSTs and cytochrome P-450s. The precise reason and molecular mechanism for this induction of GST activity is not known. One theory is that safeners cause a stress response in the plant that leads to transcriptional activation of defense genes, such as GSTs. We hope to gain insight into safener mode of action by understanding the mechanism for activation of GST gene expression in response to safeners and various plant hormones. Currently, we are examining the promoters of the GST genes from T. tauschii for regulatory elements that might be involved with transcriptional activation and increased expression following herbicide safener treatment.

Previous research mapped homoeologous copies of the GST genes to the short arms of chromosomes 6A, 6B, and 6D in cultivated wheat. Recent research findings show that only the GST genes on chromosome 6D are expressed in safener-treated wheat shoots. We plan to compare the promoters of the GST genes from 6A, 6B, and 6D to help identify critical regulatory elements involved in the safener response that might be missing from the promoters of non-responsive GST genes on chromosomes 6A and 6B.

Soybean Injury from Plant Growth Regulator (PGR) Herbicides

Several auxin-like herbicides (dicamba, clopyralid, 2,4-D) commonly used in corn for postemergence weed control can injure soybeans at extremely low rates. These plant growth regulator (PGR) herbicides can drift onto nearby soybean fields, or can be directly applied at very low rates if spray tanks are not thoroughly cleaned before spraying soybeans. These herbicides can cause severe injury to newly emerging soybean leaves, and also delayed maturity and decreased yield. Injury symptoms include leaf cupping, strapping, parallel veination, and puckering.

We are working on developing a laboratory assay to detect the presence of these PGR herbicides in soybean leaves, based on their effects on gene expression levels and expression patterns. Using molecular techniques such as RT-PCR and differential display of mRNA, we can fingerprint the expression of one or many genes in soybean leaves that have been treated with very low levels of the PGR herbicides. We hope to find a gene (or genes) that is only expressed in PGR-treated soybean leaves, and will then use the expression of this gene as a molecular marker to diagnose the presence of the herbicide. We have already found an auxin-regulated gene that is only expressed in soybean leaves treated with each of the three PGR herbicides listed above. We also hope to find specific genes that can be used to distinguish among dicamba, clopyralid, and 2,4-D.

Characterizing the Interaction Between Mesotrione and Atrazine

Broadleaf weeds such as waterhemp and kochia have evolved resistance to many different classes of herbicides, with some biotypes having 'multiple resistance', meaning resistance to more than one class of herbicides in the same plant.  HPPD-inhibiting herbicides, such as Callisto (mesotrione) and Balance Pro (isoxaflutole), are relatively new herbicides with excellent activity on these problem broadleaf weeds.  Since these herbicides have only been used in corn for a few years, weed resistance to HPPD inhibitors has not developed so far.  Callisto is often tank-mixed with a low amount of atrazine, a photosystem II inhibitor, and displays synergistic herbicidal activity on waterhemp and pigweeds when applied postemergence.  In addition to improving weed control with the Callisto plus atrazine tank mix, this weed management strategy may also aid in preventing or delaying the development of weed resistance to Callisto through the combination of herbicides having two distinct target sites and modes of action.  Interestingly, the synergism between Callisto and atrazine has also been documented in atrazine-resistant waterhemp and pigweed biotypes.  Ongoing greenhouse and laboratory studies are aimed at determining the underlying physiological basis for this interaction.

Teaching

• CPSC 426: Weed Management in Agronomic Crops

  This course will discuss principles of weed biology and ecology, chemical and non-chemical control measures, and the application of these principles towards integrated weed management in agronomic crops such as corn, soybeans, and wheat, as well as other crops grown around the world. Emphasis will be placed on applied weed management strategies in corn and soybeans. Specialized topics will include weed management in reduced tillage systems, perennial weed control, herbicide tolerant crops, herbicide resistant weeds, and management of specific problem weeds in Illinois corn and soybean production.

• CPSC 526: Herbicide Action in Plants

  This course will discuss principles of herbicide physiology and biochemistry in plants. Lecture topics will cover aspects of herbicide uptake, translocation, mechanism of action, sites of action, selectivity, metabolism, and detoxification. Special topics will include application of molecular techniques in herbicide physiology research, herbicide resistant crops and weeds, resistance mechanisms in weeds, and use of biotechnology to improve herbicide selectivity between crops and weeds. Students will lead weekly discussions to learn how to critically evaluate scientific research papers related to herbicide physiology and biochemistry.

Publications

Book Chapter

• Riechers, D.E., K.C. Vaughn, and W.T. Molin. 2005.  The role of plant glutathione S-transferases in herbicide metabolism. In Environmental Fate and Safety Management of Agrochemicals, J.M. Clark, H. Ohkawa, eds., ACS Symposium Series 899, American Chemical Society, Washington DC, pp. 216-23

Journal Articles

• Kelley, K.B., and D.E. Riechers. 2007.  Recent developments in auxin biology and new opportunities for auxinic herbicide research.  Pestic. Biochem. Physiol. (in press).
• Volenberg, D.S., P.J. Tranel, J.F. Holt, F.W. Simmons, S.C. Weller, A. Sharkhuu, and D.E. Riechers. 2007.  Assessment of two biotypes of Solanum ptycanthum that differ in resistance levels to imazamox.  Weed Res. 47:353-363.
• Zhang, Q, F.-X. Xu, K.N. Lambert, and D.E. Riechers. 2007.  Safeners coordinately induce the expression of multiple proteins and MRP transcripts involved in herbicide metabolism and detoxification in Triticum tauschii seedling tissues.  Proteomics 7:1261-1278.
• Kelley, K.B., Q. Zhang, K.N. Lambert, and D.E. Riechers. 2006.  Evaluation of auxin-responsive genes in soybean for detection of off-target plant growth regulator herbicides. Weed Sci. 54:220-229.
• Pataky, J.K., J.N. Nordby, M.M. Williams, and D.E. Riechers. 2006.  Inheritance of cross-sensitivity in sweet corn to herbicides applied postemergence.  J. Amer. Soc. Hort. Sci. 131:744-751.
• Bierman, R.E., D.E. Riechers, C.L. Sprague, G. Bollero, and W.L. Pedersen. 2006.  Fungicide-herbicide interaction in soybean (Glycine max).  Crop Prot. 25:134-139.
• Reiling, K.L., F.W. Simmons, D.E. Riechers, and L.E. Steckel. 2006.  Application timing and soil factors affect sulfentrazone phytotoxicity to two soybean (Glycine max (L.) Merr.) cultivars.  Crop Prot. 25:230-234.
• Zhou, W., F.L. Kolb, and D.E. Riechers. 2005.  Identification of proteins induced or up-regulated by Fusarium head blight infection in the spikes of hexaploid wheat (Triticum aestivum).  Genome 48:770-780.
• Williams, M.M., J.K. Pataky, J.N. Nordby, D.E. Riechers, C.L. Sprague, and J.B. Masiunas. 2005. Cross-sensitivity in sweet corn to nicosulfuron and mesotrione applied postemergence.  Hort. Sci. 40:1801-1805.
• Kelley, K.B., L.M. Wax, A.G. Hager, and D.E. Riechers. 2005.  Soybean response to plant growth regulator herbicides is affected by other postemergence herbicides.  Weed Sci. 53:101-112.
• Bunting, J.A., C.L. Sprague, and D.E. Riechers. 2005.  Incorporating foramsulfuron into annual weed control systems for corn.  Weed Technol. 19:160-167.
• Holappa, L.D., M.K. Walker-Simmons, T.H.D. Ho, D.E. Riechers, D.M. Beckles, and R.L. Jones.  2005. A Triticum tauschii protein kinase related to wheat PKABA1 is associated with ABA signaling and is distributed between the nucleus and cytosol. J. Cereal Sci. 41:333-346.
• Bunting, J.A., C.L. Sprague, and D.E. Riechers. 2004.  Proper adjuvant selection for foramsulfuron activity.  Crop Prot. 23:361-366.
• Kelley, K.B., K.N. Lambert, A.G. Hager, and D.E. Riechers. 2004.  Quantitative expression analysis of GH3, a gene induced by plant growth regulator herbicides in soybean.  J. Agric. Food Chem. 52:474-478.
• Zhang, Q., and D.E. Riechers. 2004.  Proteomic characterization of herbicide safener-induced proteins in the coleoptile of Triticum tauschii seedlings.  Proteomics 4:2058-2071.
• Bunting, J.A., C.L. Sprague, and D.E. Riechers. 2004.  Absorption and activity of foramsulfuron in giant foxtail (Setaria faberi) and woolly cupgrass (Eriochloa villosa) with various adjuvants.  Weed Sci.  52:513-517.
• Bunting, J.A., C.L. Sprague, and D. E. Riechers. 2004.  Physiological basis for tolerance of corn hybrids to foramsulfuron.  Weed Sci.  52:711-717.
• Bunting, J.A., C.L. Sprague, and D.E. Riechers.  2004.  Corn tolerance as affected by the timing of foramsulfuron applications.  Weed Technol. 18:757-762.
• Milliman, L.D., D.E. Riechers, L.M. Wax, and F.W. Simmons. 2003.  Characterization of two biotypes of imidazolinone-resistant eastern black nightshade.  Weed Sci. 51:139-144.
• Riechers, D.E., Q. Zhang, F.-X. Xu, and K.C. Vaughn. 2003.  Tissue-specific expression and localization of safener-induced glutathione S-transferase proteins in Triticum tauschii.  Planta 217:831-840.
• Xu, F.-X., E.S. Lagudah, S. P. Moose, and D.E. Riechers. 2002.  Tandemly duplicated safener-induced glutathione S-transferase genes from Triticum tauschii contribute to genome- and organ-specific expression in hexaploid wheat.  Plant Physiol. 130:362-373.
• Riechers, D.E. and M.P. Timko. 1999. Structure and expression of the gene family encoding putrescine N-methyltransferase in Nicotiana tabacum: new clues to the evolutionary origin of cultivated tobacco. Plant Mol. Biol. 41 (3):387-401, October 1999.
• Riechers, D.E., A. Kleinhofs, G.P. Irzyk, and S.S. Jones. 1998. Chromosomal location and expression of a herbicide safener-regulated glutathione S-transferase gene in Triticum aestivum and linkage relations in Hordeum vulgare. Genome 41:368-372.
• Riechers, D.E., G. P. Irzyk, E.P. Fuerst, and S.S. Jones. 1997. Nucleotide sequence of a cDNA encoding a safener-induced glutathione S-transferase (accession no. AF004358) from Triticum tauschii (PGR97-110). Plant Physiol. 114:1568.
• Riechers, D.E., G.P. Irzyk, S.S. Jones, and E.P. Fuerst. 1997. Partial characterization of glutathione S-transferases from wheat (Triticum spp.) and purification of a safener-induced glutathione S-transferase from Triticum tauschii. Plant Physiol. 114:1461-1470.
• Riechers, D.E., K. Yang, G.P. Irzyk, S.S. Jones, and E.P. Fuerst. 1996. Variability of glutathione S-transferase levels and dimethenamid tolerance in safener-treated wheat and wheat relatives. Pestic. Biochem. Physiol. 56:88-101.
• Riechers, D.E., E.P. Fuerst, and K.D. Miller. 1996. Initial metabolism of dimethenamid in safened and unsafened wheat shoots. J. Agric. Food Chem. 44:1558-1564.
• Riechers, D.E., L.M. Wax, R.A. Liebl, and D.G. Bullock. 1995. Surfactant effects on glyphosate efficacy. Weed Technol. 9:281-285.
• Riechers, D.E., L.M. Wax, R.A. Liebl, and D.R. Bush. 1994. Surfactant-increased glyphosate uptake into plasma membrane vesicles isolated from common lambsquarters leaves. Plant Physiol. 105:1419-1425.
• Wade, B.R., D.E. Riechers, R.A. Liebl, and L.M. Wax. 1993. The plasma membrane as a barrier to herbicide penetration and site for adjuvant action. Pestic. Sci. 37:195-202.
• Riechers, D.E. 1991. Herbicide resistance in weeds. J. Agron. Educ. 20:63-65.

Extension Publications

• Kelley, K., D. Riechers, D. Nordby, and A. Hager. 2004. Plant Growth Regulator Injury to Soybeans. Extension fact sheet, posted on the internet at: http://www.ipm.uiuc.edu/bulletin/article.php?issueNumber=25&issueYear=2004&articleNumber=7
• Riechers, D.E., E.P. Fuerst, and C.M. Boerboom. 1994. Advancements in the development of seed-applied herbicide safeners for wheat. Wash. State Univ. Coop. Ext. Tech. Rep. 94-6, p. 102.
• Boerboom, C.M., E.P. Fuerst, and D.E. Riechers. 1993. Wheat safener research targeted for jointed goatgrass control. Wash. State Univ. Coop. Ext. Tech. Rep. 93-4, pp. 77-78.

Invited Presentations

• "Proteomics Approaches for Studying Herbicide Safener Mechanism of Action in Triticum tauschii Seedlings", BASF BioScience Research Symposium, St. Johann, Germany.  2005.
• "Regulation and Function of Herbicide Safener-Inducible Glutathione S-Transferases in the Model Grass Species Triticum tauschii", 4th Int'l. Weed Science Congress, Durban, South Africa.  2004.
• "Role of Plant Glutathione S-Transferases in Herbicide Metabolism", 3rd Pan Pacific Conference on Pesticide Science, Honolulu, HI, June 2003.
• "Analyzing Gene Expression at the Protein Level:  Using Proteomics Techniques to Investigate Herbicide Safener Mechanism of Action", North Central Weed Science Society, Louisville, KY, December 2003.

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