1-deoxy-D-xylulose-5-phosphate synthase, a limiting enzyme for plastidic isoprenoid biosynthesis in plants

The initial step of the plastidic 2C-methyl-D-erythritol 4-phosphate (MEP) pathway that produces isopentenyl diphosphate is catalyzed by 1-deoxy-D-xyl ulose-5-phosphate synthase. To investigate whether or not 1-deoxy-D-xylulos e-5-phosphate synthase catalyzes a limiting step in the MEP pathway in plan ts, we produced transgenic Arabidopsis plants that over- or underexpress th is enzyme. Compared with non-transgenic wild-type plants, the transgenic pl ants accumulate different levels of various isoprenoids such as chlorophyll s, tocopherols, carotenoids, abscisic acid, and gibberellins. Phenotypicall y, the transgenic plants had slight alterations in growth and germination r ates. Because the levels of several plastidic isoprenoids correlate with ch anges in 1-deoxy-D-xylulose-5-phosphate synthase levels, we conclude that t his enzyme catalyzes one of the rate-limiting steps of the MEP biosynthetic pathway. Furthermore, since the product of the MEP pathway is isopentenyl diphosphate, our results suggest that in plastids the pool of isopentenyl d iphosphate is limiting to isprenoid production.