Short communication Molecular characterization of a new 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) transcript from Vanda Mimi Palmer Wai-Sun Chan a , Janna Ong Abdullah a, *, Parameswari Namasivayam b , Maziah Mahmood c a Department of Microbiology, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, UPM 43400 Serdang, Selangor Darul Ehsan, Malaysia b Department of Molecular & Cellular Biology, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, UPM 43400 Serdang, Selangor Darul Ehsan, Malaysia c Department of Biochemistry, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, UPM 43400 Serdang, Selangor Darul Ehsan, Malaysia 1. Introduction Orchidaceae is famous because of the remarkable floral diversity, the ease of cultivation, the wonderful fragrance and the diversity in pollination biology. Vanda is one of the genera in this highly diversified family. Various Vanda species and hybrids have been extensively hybridized among themselves and with other orchid genera to give rise to Vanda hybrids of different flower sizes and shapes (Rittershausen and Rittershausen, 2002). An example of a highly sought-after Vanda hybrid is Vanda Mimi Palmer. It is a hybrid of Vanda tessellata and Vanda Tan Chay Yan, and is highly scented tropical orchid which blooms all year round (The Royal Horticultural Society). In angiosperms, floral fragrance plays an important role in pollinators’ attraction and is primarily composed of terpenoids, benzenoids/phenylpropanoids and fatty acid derivatives (Pichersky et al., 2006). Analysis of orchid volatiles showed these volatile compounds were identical to insect pheromones as pollination attractants (Vaugh, 2007). In plants, terpenoids are synthesized from isoprenoids in the cytosolic mevalonate (MVA) and the plastidial 2-C-methyl-D-erythritol 4-phosphate (MEP) pathways (Hemmerlin et al., 2003). The MEP pathway involves seven enzymatic steps, in which 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) is the second enzyme and it is recognized as one of the committed steps for the formation of IPP and DMAPP, converting DXP to MEP (Proteau, 2004). It was previously reported that overexpression of DXR regulated the metabolic flux through the MEP pathway, resulting in increased levels of terpenoids in different types of plants (Mahmoud and Croteau, 2001; Hasunuma et al., 2008). Plant volatiles are complex and to date the identification of volatile compounds is far more than the isolation of fragrant- related transcripts (Schnepp and Dudareva, 2006). Thus, molecular biology studies on floral fragrance in orchids are important to understand the biology of scented orchid. So far, only one EST encoding for DXR from Orchidaceae, Phalaenopsis, had been reported and isolated (Hsiao et al., 2006). The primary goal of this study was to isolate and characterize one of the fragrant- related transcripts, DXR, identified from the floral ESTs of Vanda Mimi Palmer (VMPDXR). This is the first report on the full-length gene isolation and the expression profile of DXR in a vandaceous orchid. It is with the hope that availability of the sequence will provide an insight into gene expression during scent production and flower development of Vanda Mimi Palmer. Scientia Horticulturae 121 (2009) 378–382 ARTICLE INFO Article history: Received 22 October 2008 Received in revised form 11 February 2009 Accepted 12 February 2009 Keywords: Orchid Vanda 1-Deoxy-D-xylulose 5-phosphate reductoisomerase MEP pathway Fragrance ABSTRACT A 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) transcript was successfully isolated from the floral cDNA library of Vanda Mimi Palmer (VMPDXR). The full-length cDNA of clone VMPDXR was predicted to encode a polypeptide of 473 amino acid residues with 15 bp of 5 0 UTR and 230 bp of 3 0 UTR including a poly-A tail. VMPDXR was predicted to have a molecular mass of 51.4 kD and a pI value of 6.04. It has two conserved domains, an N-terminal NADPH binding site (GSTGSIG) and an N-terminal proline- rich region (PPPPAWPGR). It also contains two highly homologous regions, a 78–207 amino acids stretch at the N-terminal and a 221–304 amino acids stretch at the C-terminal domain. The putative plastid transit peptide is not found in VMPDXR and it is clustered into the plant DXRs in the phylogenetic tree. VMPDXR was differentially expressed in roots, leaves, sepals, petals and column. The VMPDXR transcript levels were preferentially high in blooming and fully bloomed flowers compared to the bud. The expression of VMPDXR at different times did not appear in a rhythmic manner and no drastic fluctuation was observed at night except at 2 pm during the day. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +60 3 8946 6697; fax: +60 3 89430913. E-mail address: janna@biotech.upm.edu.my (J.O. Abdullah). Abbreviations: RT-PCR, reverse-transcriptase polymerase chain reaction; DXR, 1- deoxy-D-xylulose 5-phosphate reductoisomerase; MVA, mevalonate; MEP, 2-C- methyl-D-erythritol 4-phosphate; IPP, isopentenyl diphosphate; DMAPP, dimethy- lallyl diphosphate; VMPDXR, Vanda Mimi Palmer 1-deoxy-D-xylulose 5-phosphate reductoisomerase; EST, expressed sequence tags. Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti 0304-4238/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2009.02.015