FaQR, Required for the Biosynthesis of the Strawberry Flavor Compound 4-Hydroxy-2,5-Dimethyl-3(2H)-Furanone, Encodes an Enone Oxidoreductase

• Published in: The Plant cell 2006-04, Vol.18 (4), p.1023-1037
• Main Authors: Raab, Thomas, López-Ráez, Juan Antonio, Klein, Dorothée, Caballero, Jose Luis, Moyano, Enriqueta, Schwab, Wilfried, Muñoz-Blanco, Juan
• Format: Article
• Language: English
• Subjects: 4-hydroxy-2,5-dimethyl-3(2H)-furanone; Amino Acid Sequence; amino acid sequences; Amino acids; Auxins; Biosynthesis; Biotechnology; Complementary DNA; Computational Biology; Conserved Sequence; E coli; enone oxidoreductases; Enzymatic activity; enzyme activity; Enzymes; Escherichia coli; FaQR gene; flavor compounds; Flavors; Fragaria; Fragaria - enzymology; Fragaria ananassa; Fruit; Fruits; fruits (plant anatomy); Furans - metabolism; Gels; gene expression; genes; heterocyclic oxygen compounds; Indoleacetic Acids - metabolism; Kinetics; Liquid chromatography; Mass spectrometry; messenger RNA; Molecular Sequence Data; nucleotide sequences; odor compounds; oxidoreductases; Oxidoreductases Acting on CH-CH Group Donors - chemistry; Oxidoreductases Acting on CH-CH Group Donors - genetics; Oxidoreductases Acting on CH-CH Group Donors - metabolism; Parenchyma; Peptide Fragments - chemistry; Plant Proteins - chemistry; Plant Proteins - genetics; Plant Proteins - metabolism; quinone oxidoreductase; Quinones; Reverse Transcriptase Polymerase Chain Reaction; Ripening; RNA; RNA, Plant - genetics; RNA, Plant - isolation & purification; Sequence Alignment; Sequence Homology, Amino Acid; strawberries; Taste
• ISSN: 1532-298X; 1040-4651; 1532-298X
• DOI: 10.1105/tpc.105.039784

The flavor of strawberry (Fragaria x ananassa) fruit is dominated by an uncommon group of aroma compounds with a 2,5-dimethyl-3(H)-furanone structure. We report the characterization of an enzyme involved in the biosynthesis of 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF; Furaneol), the key flavor compound in strawberries. Protein extracts were partially purified, and the observed distribution of enzymatic activity correlated with the presence of a single polypeptide of [approximately]37 kD. Sequence analysis of two peptide fragments showed total identity with the protein sequence of a strongly ripening-induced, auxin-dependent putative quinone oxidoreductase, Fragaria x ananassa quinone oxidoreductase (FaQR). The open reading frame of the FaQR cDNA consists of 969 bp encoding a 322-amino acid protein with a calculated molecular mass of 34.3 kD. Laser capture microdissection followed by RNA extraction and amplification demonstrated the presence of FaQR mRNA in parenchyma tissue of the strawberry fruit. The FaQR protein was functionally expressed in Escherichia coli, and the monomer catalyzed the formation of HDMF. After chemical synthesis and liquid chromatography-tandem mass spectrometry analysis, 4-hydroxy-5-methyl-2-methylene-3(2H)-furanone was confirmed as a substrate of FaQR and the natural precursor of HDMF. This study demonstrates the function of the FaQR enzyme in the biosynthesis of HDMF as enone oxidoreductase and provides a foundation for the improvement of strawberry flavor and the biotechnological production of HDMF.