Molecular cloning and expression profile of β-ketoacyl-acp synthase gene from tung tree (Vernicia fordii Hemsl.)

Tung tree (Vernicia fordii) is an important woody oil tree. Tung tree seeds contain 50-60% oil with approximately 80 mole ?-eleostearic acid (9 cis, 11 trans, 13 trans octadecatrienoic acid). Fatty acid synthesis is catalyzed by the concerted action of acetyl-CoA carboxylase and fatty acid synthase, a multienzyme complex including ?-ketoacyl-acyl-carrier-protein synthase (KAS). Little is known about KAS in tung tree. The objective of this study was to clone KAS genes and analyze their expression profiles in tung tree. A full-length cDNA encoding KAS III and a partial cDNA encoding KAS II were isolated from tung tree by PCR cloning using degenerate primers and rapid amplification of cDNA ends system. The full-length cDNA of VfKAS III was 1881 bp in length with an open reading frame of 1212 bp. VfKAS III genomic DNA was also isolated and sequenced, which contained 8 exons in 5403 bp length. The deduced VfKAS III protein shared approximately 80% identity with homologous KAS IIIs from other plants. Quantitative PCR analysis revealed that KAS II and KAS III were expressed in all of the tissues and organs tested but exhibited different expression patterns in tung tree. The expression levels of KAS II in young tissues were much lower than those in mature tissues, whereas the highest expression levels of KAS III were observed in young stem and young leaf. These results should facilitate further studies on the regulation of tung oil biosynthesis by KAS in tung tree.