| Research Abstract |
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.
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