Differentially expressed scent-related genes in early bloom Michelia alba

Two developmental stages of Michelia alba (cempaka putih) flower, namely, the flower bud stage (S1) (as driver) and early flower development stage (S6) (as tester) were used in this subtractive hybridization study to investigate the scent producing genes at S6. In total, 16 scent-related genes were identified, six of which belonged to the monoterpene fragrance biosynthesis pathway while the remaining belonged to the sesquiterpene, phenylpropanoid/benzenoids and the fatty acid derivatives fragrance biosynthesis pathways. The most abundantly expressed was aromatic-L-amino acid decarboxylase, followed by monoterpene glucosyltransferase, benzoyl-CoA: benzyl alcohol benzoyl transferase, methyl jasmonate esterase, cytochrome P450 monoxygenase, (-)-germacrene D synthase, NADPH dehydrogenase, carboxylesterase, esterase/lipase/thioesterase, 10-hydroxygeraniol oxidoreductase, salicyclic acid methyltransferase, sesquiterpene cyclase, orcinol O-methyltransferase, cytochrome P450 and eugenol synthase 2. Several metabolic and scent-related enzymes were also identified including 1-D-deoxyxylulose-5-phosphate synthase (DXPS), geranyl diphosphate synthase (GDPS), lipoxygenase, heat shock protein, myb-transcription factor and cold-induced glucosyl transferase. The up-regulation of DXPS and GDPS from early to full bloom stage indicated that monoterpene fragrance biosynthesis pathway was the predominant pathway. From the data obtained, we further elucidated the monoterpene fragrance biosynthesis pathway and also showed the co-existence of three other scent biosynthesis pathways, namely, sesquiterpene, phenylpropanoid/benzenoids and the fatty acid derivatives during the development of this local flower species.