Preventing Crop Injury from Herbicides with Herbicide Safeners.
A major component of my research program involves investigating the potential to alleviate crop injury from herbicides through the use of safeners. A major goal of my research is to elucidate the biochemical and molecular basis of safener mechanism of action for increasing herbicide detoxification in cereal crops. These investigations into safener mechanism of action in maize, sorghum, and wheat have resulted in a basic and more thorough understanding of how herbicide safeners function in cereal crops, as well as gain insights into inducible detoxification systems in plants. Our most recent findings have contributed significantly to understanding the genes, proteins and enzymes involved in herbicide detoxification in cereal crops, as well as towards comprehending the basic mechanism(s) of herbicide safeners for improving herbicide selectivity. For example, our recent proteomic and RNAseq results provide the framework for targeting which genes/proteins are critical for the safener responses in cereal crop coleoptiles. Recent discoveries in my lab also indicate that safeners trigger the expression of proteins in a plant defense pathway that is normally regulated by oxylipins, which are synthesized in plants from the breakdown products of lipids and oxidized fatty acids in response to stress. Tissue microdissection combined with RNAseq to analyze safener-responsive, tissue-specific transcriptomes in the outer cell layers of grain sorghum coleoptiles has led to successfully attracting funding from the USDA-NIFA to further pursue this research area.
Safener-treated sorghum shoot cross section, depicting GST subcellular localization (green) and cell nuclei (blue). Cells are outlined in red due to anti-PIN2 labeling.
Mechanisms of Evolved Weed Resistance to Herbicides.
The discovery of an HPPD-resistant waterhemp population in McLean County, IL in 2009 in a seed corn production field was of great interest to our research group. Our initial work on this population indicated that it is cross resistant to all HPPD inhibitors currently marketed in the U.S., as well as multiple resistant to atrazine and ALS inhibitors. My research group has investigated enhanced herbicide metabolism via P450s and GSTs as the mechanisms conferring resistance to mesotrione and atrazine, respectively, within this waterhemp population. This work sets the framework for control of the recently discovered HPPD-resistant waterhemp population from McLean County, IL (as well as several new HPPD-resistant waterhemp and Palmer amaranth populations throughout the Midwest) and for guiding further biochemical and molecular studies aimed at unraveling HPPD and atrazine non-target site-resistance mechanism(s) within these populations.
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.