Identification and Functional Analysis of SabHLHs in L.

L., a semi-parasitic evergreen tree, contains economically important essential oil, rich in sesquiterpenoids, such as () α- and () β-santalol. However, their transcriptional regulations are not clear. Several studies of other plants have shown that basic-helix-loop-helix (bHLH) transcription factors (TFs) were involved in participating in the biosynthesis of sesquiterpene synthase genes. Herein, bHLH TF genes with similar expression patterns and high expression levels were screened by co-expression analysis, and their full-length ORFs were obtained. These bHLH TFs were named , , , , , , , and . All eight TFs had highly conserved bHLH domains and , , , and , also had highly conserved MYC domains. It was indicated that the eight genes belonged to six subfamilies of the bHLH TF family. Among them, SaMYC1 was found in both the nucleus and the cytoplasm, while SaMYC4 was only localized in the cytoplasm and the remaining six TFs were localized in nucleus. In a yeast one-hybrid experiment, we constructed decoy vectors pAbAi-SSy1G-box, pAbAi-CYP2G-box, pAbAi-CYP3G-box, and pAbAi-CYP4G-box, which had been transformed into yeast. We also constructed pGADT7- and pGADT7- capture vectors and transformed them into bait strains. Our results showed that could bind to the G-box of and the promoter, which proved has acted as a key enzyme in the synthesis of santalol sesquiterpenes and catalyzed the ligation of santalol sesquiterpenes into terpene. We have also constructed pGreenII 62-SK-1, pGreenII 0800-LUC- and pGreenII 0800-- via dual-luciferase fusion expression vectors and transformed them into using an -mediated method. The results showed that 1 was successfully combined with or promoter and the value was 1.85- or 1.55-fold higher, respectively, than that of the control group. Therefore, we inferred that could activate both and promoters.