Mechanisms for heartwood lignan biosynthesis

本研究的最终目的是阐明心木苯丙类化合物生物合成的分子机制。在本研究中，首先，主要研究者及其同事在Chamaecyparis obtusa中调查了一种可能的心材木脂素，hinkinin的前体，并鉴定了一种新的木脂素和9种已知的木脂素，其中一些可能是hinkinin的前体木脂素。此外，通过同步饲养实验，建立了另一种典型心材木脂素yatein的生物合成途径。这项技术也被发现对代谢组学分析非常有用。其次，在之前的论文中，主要研究者和同事报道了牛蒡子和Wikstroemia sikokiana与连翘属植物合成木脂素的立体化学机制不同，本项目作为前人工作的延续，他们研究了牛蒡子、达芙妮属、炭黑属和Linum flavum varo compactum等几种植物合成木脂素的立体化学机制。结果表明，松脂醇/松脂醇还原酶的多种异构体的空间分化和物种特异性表达至少在一定程度上解释了木脂素生物合成中的立体化学多样性。其次，利用红花cDNA文库对木脂素生物合成中涉及的多个OMT进行了cDNA克隆，并成功克隆了部分OMT cDNA。目前正在使用重组酶对omt进行表征。最后，研究了另一种重要的心材物质norlignan的生物合成。因此，从苯丙类单体到去木脂素顺式扁柏树脂醇的生物合成途径首次被建立。ρ-香豆醇和ρ-香豆醇辅酶a是降木酚素的直接C6-C3前体。同时，也首次检测到去脂素合成酶的活性。

The final goal of this research is to elucidate molecular mechanisms for biosynthesis of heartwood phenylpropanoid compounds.In the present study, firsty, the principal investigator and his coworkers surveyed possible precursors of a heartwood lignan, hinokinin, in Chamaecyparis obtusa, and identified a novel lignan together with 9 known lignans, some of which are probably precursor lignans of hinokinin. In addition, the biosynthetic pathway of another typical heartwood lignan, yatein, has been established by means of cimultaneous feeding experiments. The technique has also been found to be very useful for metabolome analyses.Secondly, in the pervious papers, the principal investigator and co-workers reported the stereochemical mechanisms in lignan biosynthesis in Arctium lappa and Wikstroemia sikokiana are different from that in Forsythia spp. As the continuation of the previous works, in this research project they studied the stereochemical mechanisms in lignan biosynthesis using several plant species including Arctium lappa, Daphne spp., Anthriscus sylvestris, and Linum flavum var. compactum, and concluded that spatially differentiated and species specific expression of multiple isoforms of pinoresinol/lariciresinol reductase can account, at least in part, the stereochemical diversity in lignan biosynthesis,Next, cDNA cloning of several OMTs which are involved in lignan biosynthesis was carried out using Carthamus tinctorius cDNA library, and some OMT cDNAs have been successfully cloned. Characterizaion of the OMTs using recombinant enzymes are under way.Lastly, biosynthesis of another important heartwood substance, norlignan, was studied. Thus, a biosynthetic pathway from phenylpropanoid monomers to a norlignan, cis-hinokiresinol, has been established for the first time. ρ-coumaryl alchol and ρ-Coumaryl CoA were found to be immediate C6-C3 precursors of the norlignan. Also, norlignan synthase activity has been detected for the first time.