Description

Acetolactate synthase (ALS) is an enzyme within the plastids of plants, fungi, and bacteria. ALS is a critical enzyme within the pathway that synthesizes branched-chain amino acids of valine, leucine, and isoleucine. The enzyme ALS is the target site for many classes of commercial herbicides, including sulfonylureas (SU), imidazolines (IMI), pyrimidinyloxybenzoates (POB), and triazolopyrimidines (TP). The inhibition of ALS results in plant death due to the lack of branched-chain amino acids. While this herbicide class (Group 2) has had major successes in controlling weeds in many crop systems, there is widespread resistance due to long-term selection pressures in the field.

Group 2 resistance in weeds can be caused by point mutations (nucleotide substitutions) within the ALS gene that change specific amino acids that make up the enzyme. These amino acid changes prevent the herbicide from binding to its target, yet the enzyme remains functional within the plant because these mutations are not within the enzyme’s catalytic site. Compared to other resistant mechanisms for additional herbicide classes, it appears that many of these substitutions/mutations in the ALS enzyme do not result in fitness penalties to individual plants. However, specific mutations do vary in their level of protection for certain herbicide treatments.

NAGC optimized and validated a DNA-based test for screening of altered sites within the ALS gene using a combination of published assays and bioinformatic analysis from a collaborative greenhouse and genetic testing project with NDSU weed scientists.

This rapid genotyping test detects a common mutation within the ALS gene, where an amino acid change from the wildtype W (Tryptophan) to the mutant L (Leucine) confers resistance to Group 2 or ALS-inhibiting herbicides in most Amaranthus (pigweed) species found within North America.

This project was funded by the North Dakota Corn Utilization Council, North Dakota Soybean Council, and North Dakota Department of Agriculture.