Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore 117604, Singapore.
Department of Biological Sciences, National University of Singapore, Singapore 117543, Singapore.
Int J Mol Sci. 2020 Nov 13;21(22):8566. doi: 10.3390/ijms21228566.
In addition to the well-known diterpenoid steviol glycosides, (Stevia) produces many labdane-type diterpenoids and a wide range of mono- and sesquiterpenoids. However, biosynthesis of mono- and sesquiterpenoids in Stevia remains unknown. Here we analyzed the extracts of Stevia leaves, flowers, stems, and roots by Gas Chromatography-Mass Spectrometry and putatively identified a total of 69 volatile organic compounds, most of which were terpenoids with considerably varied quantities among the four tissues of Stevia. Using Stevia transcriptomes, we identified and functionally characterized five terpene synthases (TPSs) that produced major mono- and sesquiterpenoids in Stevia. Transcript levels of these Stevia s and levels of corresponding terpenoids correlated well in Stevia tissues. Particularly, the root-specific SrTPS4 and SrTPS5 catalyzed the formation of γ-curcumene/zingiberene/β-sesquiphellandrene and α-longipinene/β-himachalene/himachalol as multifunctional sesqui-TPSs, respectively. Most of the were highly responsive to various environmental stresses in a tissue-specific manner. Taken together, our results provide new insights into how Stevia produces diverse terpenoids to confer differential responses to various environmental factors in each tissue.
除了众所周知的二萜甜菊糖苷外，（甜叶菊）还产生许多贝壳杉烷型二萜和广泛的单萜和倍半萜。然而，甜叶菊中单萜和倍半萜的生物合成仍不清楚。在这里，我们通过气相色谱-质谱法分析了甜叶菊叶、花、茎和根的提取物，推测共鉴定出 69 种挥发性有机化合物，其中大多数为萜类化合物，在甜叶菊的四种组织中数量差异很大。利用甜叶菊转录组，我们鉴定并功能表征了产生甜叶菊主要单萜和倍半萜的五个萜烯合酶（TPS）。这些甜叶菊的转录水平和相应萜类化合物的水平在甜叶菊组织中相关性良好。特别是，根特异性 SrTPS4 和 SrTPS5 分别作为多功能倍半萜 TPS，催化 γ-姜黄烯/姜烯/β-大根香叶烯和 α-长叶薄荷烯/β-喜马拉雅烯/异胡薄荷醇的形成。大多数萜类化合物对各种环境胁迫具有高度的组织特异性响应。总之，我们的结果提供了新的见解，即甜叶菊如何产生不同的萜类化合物，以在每种组织中对各种环境因素产生不同的响应。
