4-Hydroxybenzoate polyprenyl diphosphate transferase (4HPT) is the key enzyme that transfers the prenyl side chain to the benzoquione frame in ubiquinone (UQ) biosynthesis. The Arabidopsis AtPPT1 cDNA encoding 4HPT was cloned by reverse transcription-polymerase chain reaction (RT-PCR) based on the information of the Arabidopsis genomic sequence, and the function of the gene was determined. Heterologous expression of the AtPPT1 gene enabled restoration of the respiratory ability and UQ synthesis in a yeast mutant that was defective in 4HPT activity. The mitochondrial fraction that was prepared from the yeast mutant, which expressed the AtPPT1 gene, exhibited 4HPT enzymatic activity with geranyl diphosphate (GPP) as the prenyl substrate. This indicated that the AtPPT1 gene encodes active 4HPT with a broad substrate specificity in terms of the prenyl donor. The AtPPT1 mRNA was predominantly expressed in the flower cluster, and the green fluorescent protein (GFP) fused with the signal peptide of AtPPT1 was translocated into the mitochondria. T-DNA insertion mutation that disrupts the AtPPT1 gene in Arabidopsis resulted in the arrest of embryo development at an early stage of zygotic embryogenesis. These results demonstrate that the AtPPT1 gene involved in the biosynthesis of mitochondrial UQ plays an essential role in embryo development in Arabidopsis .