Herbicide sensitivity determinant of wheat plastid acetyl-CoA carboxylase is located in a 400-amino acid fragment of the carboxyltransferase domain

A series of chimeral genes, consisting of the yeast GAL10 promoter. yeast A CC1 leader, wheat acetyl-CoA carboxylase (ACCase; EC 6.4.1.2) cDNA, and yea st ACC1 3'-tail. was used to complement a yeast ACC1 mutation. These genes encode a full-length plastid enzyme, with and without the putative chloropl ast transit peptide, as well as five chimeric cytosolic/plastid proteins. F our of the genes, all containing at least half of the wheat cytosolic ACCas e coding region at the 5'-end, complement the yeast mutation. Aryloxyphenox ypropionate and cyclohexanedione herbicides. at concentrations below 10 mu M, inhibit the growth of haploid yeast strains that express two of the chim eric ACCases. This inhibition resembles the inhibition of wheat plastid ACC ase observed in vitro and in vivo. The differential response to herbicides localizes the sensitivity determinant to the third quarter of the multidoma in plastid ACCase. Sequence comparisons of different multidomain and multis ubunit ACCases suggest that this region includes part of the carboxyltransf erase domain, and therefore that the carboxyltransferase activity of ACCase (second half-reaction) is the target of the inhibitors. The highly sensiti ve yeast gene-replacement strains described here provide a convenient syste m to study herbicide interaction with the enzyme and a powerful screening s ystem for new inhibitors.