3-Hydroxy-3-methylglutaryl-coenzyme A reductase from Arabidopsis thaliana is structurally distinct from the yeast and animal enzymes.

We have isolated the Arabidopsis thaliana gene (HMG1) encoding 3-hydroxy-3-methylglutaryl-CoA reductase [HMG-CoA reductase; (S)-mevalonate:NAD+ oxido-reductase (CoA-acylating), EC 1.1.1.88], the catalyst of the first committed step in isoprenoid biosynthesis. cDNA copies of the plant gene were identified by hybridization with a short, highly conserved segment of yeast HMG-CoA reductase as probe. DNA sequence analysis reveals that the COOH-terminal domain of the Arabidopsis HMG-CoA reductase (containing the catalytic site of the enzyme) is highly conserved with respect to the yeast, mammalian, and Drosophila enzymes, whereas the membrane-bound amino terminus of the Arabidopsis protein is truncated and lacks the complex membrane-spanning architecture of the yeast and animal reductases. Expression of the Arabidopsis gene from the yeast GAL1 promoter in a yeast mutant lacking HMG-CoA reductase activity suppresses the growth defect of the yeast mutant. Taken together, the sequence similarity to other cloned HMG-CoA reductase genes and the suppression of the yeast hmg- mutant provide strong evidence that the novel Arabidopsis gene we have cloned encodes a functional HMG-CoA reductase enzyme.