Department of Plant Sciences, University of Tennessee, Knoxville, TN, 37996, USA; School of Life Sciences, Anhui Agricultural University, Hefei, 230036, China.
Department of Plant Sciences, University of Tennessee, Knoxville, TN, 37996, USA.
Phytochemistry. 2021 Oct;190:112847. doi: 10.1016/j.phytochem.2021.112847. Epub 2021 Jul 6.
Liverworts (Marchantiophyta) are among the earliest diverging lineages of extant land plants. Among their unique features, most liverworts contain membrane-bound oil bodies, organelles that accumulate diverse secondary metabolites, especially terpenoids. In contrast to the rich information on liverwort terpenoid chemistry, little is known about their biosynthesis. Recently, terpenoid biosynthesis was studied in a model thalloid species Marchantiapolymorpha, in which sesquiterpenes and monoterpenes are biosynthesized by a new type of terpene synthases termed microbial terpene synthase-like (MTPSL) proteins. Here we study terpenoid biosynthesis in a leafy liverwort Radula lindenbergiana. Vegetative plants of R.lindenbergiana were found to contain a mixture of sesquiterpenes, with (E,E)-α-farnesene/β-curcumene and (Z)-β-bisabolene being the most abundant constituents. From the analysis of the R. lindenbergiana transcriptome, five full-length MTPSL genes were identified. They were designated RlMTPSL1-5, respectively. Recombinant RlMTPSL proteins were produced in Escherichia coli and tested for sesquiterpene synthase activities using farnesyl diphosphate (FPP) as substrate. All except RlMTPSL5 were demonstrated to catalyze the formation of different sesquiterpenes. RlMTPSL1 produced multiple sesquiterpenes with eremophilene and an unidentified sesquiterpene as major products. The major products of RlMTPSL2 and RlMTPSL3 were β-elemene and an unidentified sesquiterpene, respectively. RlMTPSL4 was also a multi-product sesquiterpene synthase with an unidentified sesquiterpene being the major product. Homology-based structural modeling was performed to understand the structural basis underlying different product profiles of the RlMTPSLs proteins. Most of the sesquiterpene products of the four active RlMTPSLs were also detected in R. lindenbergiana plants. Expression levels of the four RlMTPSL genes encoding active enzymes in vegetative plants were compared. In phylogenetic analysis, RlMTPSL genes were found to cluster together, indicating lineage-specific expansion of MTPSL genes in lineages leading to R.lindenbergiana and M. polymorpha. This study strengthens evidence for the contribution of MTPSL genes to terpenoid biosynthesis in liverworts.
地钱门植物（Marchantiophyta）是现存陆生植物中最早分化的谱系之一。在地钱门植物的独特特征中，大多数地钱门植物含有膜结合的油体，这是一种积累各种次生代谢产物的细胞器，特别是萜类化合物。与丰富的地钱门萜类化学信息相比，对地钱门萜类化合物的生物合成知之甚少。最近，在一种模式片状地钱门植物 Marchantiapolymorpha 中对地钱门萜类化合物的生物合成进行了研究，其中倍半萜和单萜类化合物是由一种新型萜烯合酶——微生物萜烯合酶样（MTPSL）蛋白合成的。本文研究了叶状地钱 Radula lindenbergiana 的萜类化合物生物合成。发现 R.lindenbergiana 的营养植物中含有混合的倍半萜类化合物，其中（E,E）-α-法呢烯/β-姜黄烯和（Z）-β-毕澄茄烯是最丰富的成分。通过对 R. lindenbergiana 转录组的分析，鉴定出了五个全长 MTPSL 基因。它们分别被命名为 RlMTPSL1-5。在大肠杆菌中表达了重组 RlMTPSL 蛋白，并使用法呢基二磷酸（FPP）作为底物测试了它们的倍半萜合酶活性。除了 RlMTPSL5 之外，其他所有蛋白都被证明能够催化不同倍半萜的形成。RlMTPSL1 产生了多种倍半萜类化合物，其中以大根香叶烯和一种未鉴定的倍半萜类化合物为主要产物。RlMTPSL2 和 RlMTPSL3 的主要产物分别是β-榄香烯和一种未鉴定的倍半萜类化合物。RlMTPSL4 也是一种多产物倍半萜合酶，以一种未鉴定的倍半萜类化合物为主要产物。进行了基于同源性的结构建模，以了解 RlMTPSLs 蛋白不同产物谱的结构基础。在 R. lindenbergiana 植物中也检测到了这四种有活性的 RlMTPSLs 产生的大多数倍半萜类化合物。比较了营养植物中编码有活性酶的四个 RlMTPSL 基因的表达水平。在系统发育分析中，发现 RlMTPSL 基因聚集在一起，表明 MTPSL 基因在导致 R.lindenbergiana 和 M.polymorpha 的谱系中发生了谱系特异性扩张。这项研究为 MTPSL 基因对地钱门植物萜类化合物生物合成的贡献提供了更有力的证据。
