Involved in the supply of solanesyl diphosphate for ubiquinone-9 (UQ-9) biosynthesis in mitochondria. Farnesyl diphosphate is the preferred substrate. (2E)-geranyl diphosphate + 7 isopentenyl diphosphate = all-trans-nonaprenyl diphosphate + 7 diphosphate Binds 2 Mg(2+) ions per subunit. Cofactor biosynthesis; ubiquinone biosynthesis. Homodimer. Expressed in leaves, stems and roots. Highest expression in roots. Belongs to the FPP/GGPP synthase family.