Molecular cloning and expression of a cDNA encoding 1-deoxy- d-xylulose-5-phosphate synthase from oil palm Elaeis guineensis Jacq.

Abstract

In higher plants, there are two pathways leading to the formation of isoprenoids: the acetate/mevalonate (MVA) pathway and the recently discovered 2C-methyl- d-erythritol-4-phosphate (MEP) pathway. The initial step on the MEP pathway is the condensation of pyruvate and glyceraldehyde-3-phosphate yielding 1-deoxy- d-xylulose-5-phosphate (DXP). The reaction is catalyzed by 1-deoxy- d-xylulose-5-phosphate synthase (DXS), and is encoded by the dxs gene. In this study, parts of dxs have been cloned from young leaves and mesocarp of oil palm ( Elaeis guineensis Jacq., Tenera) The surprising results show that there are at least two dxs genes encoding DXS in different organs of oil palm, dxs1 in leaves and dxs2 in fruits. Cloning of full-length cDNA encoding dxs1 by the RLM-RACE (RNA ligase-mediated rapid amplification of 5 ′ and 3 ′ cDNA ends) method demonstrated that the cDNA contained an open reading frame of 2301 bp encoding a deduced peptide of 707 amino acid residues with a predicted molecular mass of 76.4 kDa and isoelectric point of 7.0. Expression of dxs2 and dxr transcript levels in oil palm fruits from each developmental stage were analyzed by a semiquantitative RT-PCR method. The level of dxs2 transcripts increases with the time after fertilization and reaches its maximum after 18 weeks while the expression of dxr is unchanged. The pattern of dxs2 transcripts appears to correlate with β-carotene accumulation during oil palm fruit ripening thus supports the assumed role of the dxs gene in carotenoid biosynthesis by the MEP pathway.