Molecular Cloning and Functional Characterization of a Cytochrome P450 Enzyme (SaCYP736A167) Promoter from Santalum album

The primary constituents of the essential oil derived from Santalum album L. are (Z)-α-santalol, (Z)-β-santalol, (Z)-α-exo-bergamotol, and (Z)-epi-β- santalol. SaCYP736A167 plays a pivotal role in the biosynthesis of these sesquiterpene alcohols within S. album, but the mechanisms governing the expression of the SaCYP736A167 gene is far from being deciphered. In this research, a promoter sequence of the SaCYP736A167 gene, spanning 2808 base pairs, was isolated from S. album. A bioinformatics analysis of the 2384-bp SaCYP736A167 promoter (PSaCYP736A167) showed that abundant stress-inducible cis-acting elements were distributed in different regions of PSaCYP736A167. The histochemical β-glucuronidase (GUS) staining of T1 transgenic Nicotiana tabacum plants harboring PSaCYP736A167 demonstrated that the predominant GUS activity was exhibited in the parenchyma cells of the stem cortex and phloem, suggesting that PSaCYP736A167 is a tissue-specific expression promoter. GUS fluorometric assays of transiently transgenic N. benthamiana leaves revealed that seven distinct segments of PSaCYP736A167 exhibited notably varied levels of GUS activity. A 936-base pair sequence upstream of the transcription initiation codon ATG constitutes the core promoter section of PSaCYP736A167. Our findings shed light on the regulatory mechanisms controlling the transcription of the SaCYP736A167 gene, potentially serving as a novel tissue-specific promoter for applications in transgenic plant biotechnology.