Isolated polynucleotides that encode acetohydroxyacid synthase small subunit (AHASS) polypeptides, and the amino acid sequences encoding these polypeptides, are described. Expression cassettes and expression vectors comprising the polynucleotides of the invention, as well as plants and host cells transformed with the polynucleotides, expression cassettes, and expression vectors, are described. Methods of using the polynucleotides to enhance the resistance of plants to herbicides are also described.