MOLECULAR CLONING OF AN ACETYL-COENZYME A CARBOXYLASE DOMAIN FROM HERBICIDE-RESISTANT AND -SUSCEPTIBLE WILD OAT BIOTYPES

Department of Plant Sciences, North Dakota State University, Fargo, ND 58105-5051 USA

Herbicides that inhibit acetyl-coenzyme A carboxylase (ACCase; EC 6.4.1.2), i.e., those of the aryloxyphenoxypropionate and cyclohexanedione herbicide classes, are important crop production tools for selective control of wild oat (Avena fatua L.) and other weeds of the Gramineae. Both cytosolic and plastid-localized forms of ACCase from the Gramineae are multifunctional enzymes with domains for biotin carboxylation and carboxyl transfer to acetyl-coenzyme A. The carboxyl transfer reaction is disrupted by ACCase inhibiting herbicides, most likely through herbicide interaction at or near the acetyl-coenzyme A binding domain of the plastid-localized form. Several examples of wild oat resistant to ACCase inhibiting herbicides have been observed and, where studied, resistance has been associated with the herbicide target site. The field management of wild oat resistant to ACCase inhibitors would be enhanced by the development of a genetic test to confirm and classify resistance at the molecular level. To identify molecular mutations responsible for resistance, we have used the polymerase chain reaction (PCR) to amplify and clone a 521 bp region encompassing the acetyl-coenzyme A binding domain of ACCase from wild oat resistant and susceptible to ACCase inhibiting herbicides. PCR primers were targeted to plastid-localized ACCase and were designed from GenBank loci AF029895 and TAACCASEA from wheat (Triticum aestivum L.); ZMACOAC, ZMU58598, and ZMU19183 from maize (Zea mays L.); and A47134 from cultivated oat (Avena sativa L.). Sequence information allowing a comparison of herbicide-resistant and -susceptible wild oat biotypes will be presented.