Nucleotide sequence of a mutant acetolactate synthase gene from an imidazolinone-resistant Arabidopsis thaliana var. Columbia

Acetolactate synthase (ALS) is the key enzyme in the biosynthesis of leucine, isoleucine, and valine. ALS is inhibited by three groups of herbicides: imidazolinones, sulfonylureas, and triazolo pyrimidines. To understand the molecular basis of imidazolinone herbicide resistance, a mutant GH-90 of Arabidopsis thaliana , isolated and characterized by Drs. George Haughn and Chris Somerville was analyzed. The mutant plant and its ALS are 100 times more resistant to the imidazolinone herbicide imazapyr than the wild type. A genomic DNA library was constructed from the GH-90 DNA in the lambda vector EMBL3 and screened by an ALS gene probe.