The invention provides nucleic acids encoding mutants of the acetohydroxyacid synthase (AHAS) large subunit comprising at least two mutations, for example double and triple mutants, which are useful for producing transgenic or non-transgenic plants with improved levels of tolerance to AHAS-inhibiting herbicides. The invention also provides expression vectors, cells, plants comprising the polynucleotides encoding the AHAS large subunit double and triple mutants, plants comprising two or more AHAS large subunit single mutant polypeptides, and methods for making and using the same.
