MULTIPLE RESISTANCE TO SULFONYLUREAS AND IMIDAZOLINONES CONFERRED BY AN ACETOHYDROXY ACID SYNTHASE GENE WITH SEPARATE MUTATIONS FOR SELECTIVE RESISTANCE

The acetohydroxyacid synthase (AHAS) gene from the Arabidopsis thalian a mutant line GH90 carrying the imidazolinone resistance allele imr1 w as cloned. Expression of the AHAS gene under the control of the CaMV 3 5S promoter in transgenic tobacco resulted in selective imidazolinone resistance, confirming that the single base-pair change found near the 3' end of the coding region of this gene is responsible for imidazoli none resistance. A chimeric AHAS gene containing both the imr1 mutatio n and the csr1 mutation, responsible for selective resistance to sulfo nylurea herbicides, was constructed. It conferred on transgenic tobacc o plants resistance to both sulfonylurea and imidazolinone herbicides. The data illustrate that a multiple-resistance phenotype can be achie ved in an AHAS gene through combinations of separate mutations, each o f which individually confers resistance to only one class of herbicide s.