WHEAT CYTOSOLIC ACETYL-COA CARBOXYLASE COMPLEMENTS AN ACC1 NULL MUTATION IN YEAST

Spores harboring an ACC1 deletion derived from a diploid Saccharomyces cerevisiae strain, in which one copy of the entire ACC1 gene is repla ced with a LEU2 cassette, fail to grow, A chimeric gene consisting of the yeast GAL10 promoter, yeast ACC1 leader, wheat cytosolic acetyl-Co A carboxylase (ACCase) cDNA, and yeast ACC1 3' tail was used to comple ment a yeast ACC1 mutation. The complementation demonstrates that acti ve wheat ACCase can be produced in yeast, At low concentrations of gal actose, the activity of the ''wheat gene'' driven by the GAL10 promote r is low and ACCase becomes limiting for growth, a condition expected to enhance transgenic yeast sensitivity to wheat ACCase-specific inhib itors. An aryloxyphenoxypropionate and two cyclohexanediones do not in hibit growth of haploid yeast strains containing the yeast ACC1 gene, but one cyclohexanedione inhibits growth of the gene-replacement strai ns at concentrations below 0.2 mM, In vitro, the activity of wheat cyt osolic ACCase produced by the gene-replacement yeast strain is inhibit ed by haloxyfop and cethoxydim at concentrations above 0.02 mM, The ac tivity of yeast ACCase is less affected, The wheat plastid ACCase in w heat germ extract is inhibited by all three herbicides at concentratio ns below 0.02 mM. Yeast gene-replacement strains will provide a conven ient system for the study of plant ACCases.