This invention relates to an isolated nucleic acid fragment encoding an isopentenyl diphosphate biosynthetic enzyme. The invention also relates to the construction of a chimeric gene encoding all or a portion of the isopentenyl diphosphate biosynthetic enzyme, in sense or antisense orientation, wherein expression of the chimeric gene results in production of altered levels of the isopentenyl diphosphate biosynthetic enzyme in a transformed host cell.