Identification and Functional Analysis of SabHLHs in Santalum album L

Ting Zhang; Xiaohong Chen; Yuping Xiong; Meiyun Niu; Yueya Zhang; Haifeng Yan; Yuan Li; Xinhua Zhang; Guohua Ma

doi:10.3390/life12071017

Identification and Functional Analysis of SabHLHs in Santalum album L

Life (Basel). 2022 Jul 8;12(7):1017. doi: 10.3390/life12071017.

Authors

Ting Zhang^{1

2}, Xiaohong Chen^{1

2}, Yuping Xiong¹, Meiyun Niu^{1

2}, Yueya Zhang^{1

2}, Haifeng Yan³, Yuan Li¹, Xinhua Zhang¹, Guohua Ma¹

Affiliations

¹ Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, The Chinese Academy of Sciences, Guangzhou 510650, China.
² University of the Chinese Academy of Sciences, Beijing 100049, China.
³ Cash Crop Institute of Guangxi Academy of Agricultural Sciences, Nanning 530007, China.

Abstract

Santalum album L., a semi-parasitic evergreen tree, contains economically important essential oil, rich in sesquiterpenoids, such as (Z) α- and (Z) 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 SaMYC1, SaMYC3, SaMYC4, SaMYC5, SabHLH1, SabHLH2, SabHLH3, and SabHLH4. All eight TFs had highly conserved bHLH domains and SaMYC1, SaMYC3, SaMYC4, and SaMYC5, 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-SaMYC1 and pGADT7-SabHLH1 capture vectors and transformed them into bait strains. Our results showed that SaMYC1 could bind to the G-box of SaSSy, and the SaCYP736A167 promoter, which SaSSy proved has acted as a key enzyme in the synthesis of santalol sesquiterpenes and SaCYP450 catalyzed the ligation of santalol sesquiterpenes into terpene. We have also constructed pGreenII 62-SK-SaMYC1, pGreenII 0800-LUC-SaSSy and pGreenII 0800-LUC-SaCYP736A167 via dual-luciferase fusion expression vectors and transformed them into Nicotiana benthamiana using an Agrobacterium-mediated method. The results showed that SaMYC1 was successfully combined with SaSSy or SaCYP736A167 promoter and the LUC/REN value was 1.85- or 1.55-fold higher, respectively, than that of the control group. Therefore, we inferred that SaMYC1 could activate both SaSSy and SaCYP736A167 promoters.

Keywords: SaCYP736A167; SaSSy; bHLH transcription factor; dual luciferase; dual luciferase activity; gene cloning; sandalwood; subcellular localization; yeast one-hybridization.

Grants and funding

This work was financially supported by Guangdong Key Areas Biosafety Project (2022B1111040003), National Key Research & Development Program of China (2021YFC3100400) and the National Natural Science Foundation of China (grant numbers 32171841, 32101512 and 32100311).