Cloning and functional analysis of the promoterof the sesquiterpene synthase gene ASS1 in Aquilaria sinensis

Agarwood, the resin part of Aquilaria spp., is valued in medicine, perfumes, and incense. The most important components of agarwood are sesquiterpenes, which are produced only when a healthy tree is wounded. Agarwood sesquiterpene synthase 1 (ASS1) is one of key enzymes responsible for the biosynthesis of sesquiterpenes in Aquilaria sinensis (Lour.) Gilg, and it is a typical wound-inducible synthase. To elucidate its regulatory mechanism at the transcriptional level, a 978-bp sequence upstream of the translation initiation codon ATG of the promoter for ASS1 was cloned. Computational analysis revealed that this promoter contained many known cis-elements including several defense related transcriptional factor-binding boxes. To functionally validate the promoter, a 5' truncated fragment fused with the β-glucuronidase (GUS) reporter gene was used for generating stable transgenic Arabidopsis plants. The spatial and temporal expression patterns of GUS in transgenic Arabidopsis showed that the promoter of ASS1 was induced by mechanical wound and mainly expressed in vascular bundles. Subcellular localization showed that ASS1 localized in the nucleus and plasma membrane. Here, identification of the ASS1 promoter not only lays a foundation for studying its transcriptional regulation, but also provides clues for studying the synthesis mechanism of agarwood sesquiterpenes.