Molecular Cloning and Functional Analysis of 1-Deoxy-D-Xylulose 5-Phosphate Reductoisomerase from Santalum album.

Yueya Zhang,Jaime A Teixeira Da Silva,Yuping Xiong,Guohua Ma,Meiyun Niu,Yuan Li,Haifeng Yan,Xinhua Zhang

doi:10.3390/genes12050626

Abstract

Sandalwood (Santalum album L.) heartwood-derived essential oil contains a high content of sesquiterpenoids that are economically highly valued and widely used in the fragrance industry. Sesquiterpenoids are biosynthesized via the mevalonate acid and methylerythritol phosphate (MEP) pathways, which are also the sources of precursors for photosynthetic pigments. 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) is a secondary rate-limiting enzyme in the MEP pathway. In this paper, the 1416-bp open reading frame of SaDXR and its 897-bp promoter region, which contains putative conserved cis-elements involved in stress responsiveness (HSE and TC-rich repeats), hormone signaling (abscisic acid, gibberellin and salicylic acid) and light responsiveness, were cloned from 7-year-old S. album trees. A bioinformatics analysis suggested that SaDXR encodes a functional and conserved DXR protein. SaDXR was widely expressed in multiple tissues, including roots, twigs, stem sapwood, leaves, flowers, fruit and stem heartwood, displaying significantly higher levels in tissues with photosynthetic pigments, like twigs, leaves and flowers. SaDXR mRNA expression increased in etiolated seedlings exposed to light, and the content of chlorophylls and carotenoids was enhanced in all 35S::SaDXR transgenic Arabidopsis thaliana lines, consistent with the SaDXR expression level. SaDXR was also stimulated by MeJA and H2O2 in seedling roots. α-Santalol content decreased in response to fosmidomycin, a DXR inhibitor. These results suggest that SaDXR plays an important role in the biosynthesis of photosynthetic pigments, shifting the flux to sandalwood-specific sesquiterpenoids.

Highlights

Santalum album is an economically important tropical woody species of the Santalaceae family that is well known for its aromatic heartwood and essential oil [1]
We studied D-xylulose5-phosphate reductoisomerase (DXR) to better understand the biosynthesis of sesquiterpenoids and photosynthetic pigments in sandalwood
Apart from L5, other overexpression lines had a higher carotenoid content than wild type (WT) plants. These results suggest that SaDXR derived from the methylerythritol phosphate (MEP) pathway was involved in the biosynthesis of plastidial isoprenoids

Summary

Introduction

Santalum album is an economically important tropical woody species of the Santalaceae family that is well known for its aromatic heartwood and essential oil [1]. The sesquiterpenoid alcohols (Z)-α-santalol, (Z)-β-santalol, (Z)-epi-β-santalol and (Z)-α-exo-bergamotol, which are the main components of S. album essential oil, play a vital fragrance-defining role in the fragrance industry [2] These sandalwood sesquiterpenoids possess various biological properties [3]. Compared to the long cycle times associated with artificially planting sandalwood and laboriously harvesting and processing the heartwood, or the expensive cost of chemical synthesis of sandalwood sesquiterpenoids, metabolic engineering is a more economic and efficient system [4,5]. For this reason, it is critical to elucidate the molecular mechanism underlying the biosynthesis of sandalwood terpenoids

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Conclusion