Temporal regulation of two isoforms of cDNA clones encoding delta 9-stearoyl–ACP desaturase from oil palm ( Elaies guineensis)

Abstract

Stearoyl–ACP desaturase (EC 1.14.99.6) converts stearoyl–ACP to oleoyl–ACP in the fatty acid biosynthetic pathway in plants and the cDNA clones of this enzyme have been isolated and sequenced in several oil producing species such as rapeseed and safflower. However, although oil palm is the second most important source of plant lipids, not much is known about the fatty acid biosynthesis in the plant. As an initial step toward the understanding the role of stearoyl–ACP desaturase in oil palm, we have screened a 15-week mesocarp cDNA library of the commercially grown Elaeis guineensis, var Tenera. Restriction analyses carried out on three putative clones designated pTD7, pTD8 and pTD9, showed that two of the clones, pTD7 and pTD9 are similar and pTD8 had a different insert compared with the other two clones. The complete nucleotide sequences were obtained for clones pTD7 and pTD8. Comparison between the two sequences confirms the differences between the two clones with 93.5 and 95% identity at the nucleotide and amino acid level, respectively. Clones pTD7 and pTD8 are thought to be isoforms of the gene encoding stearoyl–ACP desaturase. As analysis showed that both clones contain the partial sequence, a complete sequence for stearoyl–ACP desaturase gene was isolated using a PCR-based method, using the sequence of pTD7 as a primer. The complete sequence is shown to be 1709 bp long. Both the isoforms, pTD7 and pTD8 are shown to be developmentally regulated in the developing mesocarp of the Tenera, being highly expressed at 17 and 20 weeks after anthesis, corresponding to the period of active oil synthesis. This is the first documentation of the isolation, complete sequencing and temporal regulation of a gene involved in fatty acid synthesis in oil palm. It also documents the identification and characterisation of two isoforms of the delta-9 stearoyl desaturase.