Sakakibara, Norikazu

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TitleMetabolic Analysis of the Cinnamate/Monolignol and LignanPathways(ABSTRACTS (PH D FOR GRADUATE SCHOOLOF AGRICULTURE))Author(s)Sakakibara, NorikazuCitationSustainable humanosphere : bulletin of Research Institute forSustainable Humanosphere Kyoto University (2005), 1: 24-25Issue Date2005-08-31URL http://hdl.handle.net/2433/51154RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversityABSTRACTS (PH D FOR GRADUATE SCHOOL OF AGRICULTURE)Metabolic Analysis of the Cinnamate/Monolignol and Lignan PathwaysNorikazu SakakibaraLaboratory ofMetabolic Science ofForest Plants and Microorganisms, RISH, Kyoto UniversityFossil resource-based industrial society has provided us prosperity, especially in the developedcountries. However, it also has brought serious negative impacts on the global environment due to theincrease in the atmospheric concentration of carbon dioxide, accompanied by a number of pollutionproblems. Therefore, it is becoming very important to establish a sustainable and recycling-based society,which depends on renewable resources.Wood biomass is the most abundant and potentially renewable resource. However, utilization of woodbiomass has been based on the paradigm of a fossil resource-based society. Therefore, it is necessary toestablish the sustainable production and utilization system for forest resources, so that a sustainable,recycling-based society can be established.Wood biomass is composed mostly of secondary xylem which is formed through two metabolicevents, cell-wall formation and heartwood formation. Hence, biochemical and molecular biological studiesof secondary xylem formation provide the basic knowledge for establishing systems for sustainableproduction of forest resources or wood biomass.Because both cell wall and heartwood formation comprise a wide variety of biochemical reactions, itis not an easy task to elucidate their integrated biochemical and molecular biological mechanisms.Fortunately, however, phenylpropanoid biosynthesis occurs commonly in both cell wall and heartwoodformation as principal metabolic events. For example, lignin is one of the major cell wall components,while lignans and norlignans are deposited in significant amounts in heartwood regions of trees.During the last decade, due to the recent development of molecular biological techniques, significantadvances have been made in the biosynthetic studies of phenylpropanoid. This has presented many newquestions to be elucidated in this field. For example, phenylpropanoid biosynthesis involves severalpathways where many possible and parallel routes can be envisaged, and identification of a true,physiological route among the possibilities are still open to question.In the present study, the author focused on the identification of the physiological route by the use ofcomprehensive metabolite quantitation (metabolic profiling). First, the author worked on the biosyntheticroute for yatein from matairesinol in the lignan pathway [1], and then characterizing thecinnamate/monolignol pathway in relation to lignan biosynthesis [2].A dibenzylbutyrolactone lignan, yatein, is of interest because it is not only a typical heartwood lignanbut also a key biosynthetic intermediate for an antitumor lignan, podophyllotoxin. In 1980s, it was shownthat matairesinol was a precursor of podophyllotoxin [3]. Later, the biosynthesis of matairesinol fromconiferyl alcohol was established [3]. However, the route from matairesinol to yatein remains unknown.The conversion of matairesinol to yatein involves four steps, and many possible orders of their occurrencecan be envisaged, suggesting that a metabolic grid might be present in the transformation.First of all, the author synthesized deuterium-labeled and unlabeled standards for 10 lignans which arethe possible precursors of yatein. Then, using these standards, the author established a comprehensivequantitation system for the precursors of yatein based on a stable-isotope-dilution method.The system was applied to characterizing the yatein biosynthesis in Anthriscus sylvestris, whichcontains significant amounts of yatein and other lignans. In addition, deuterium-labeled lignan and[U-ring-13C6]phenylalanine were administered to the plant, and stable isotope incorporation intodownstream metabolites were examined comprehensively. Taken together, the results of these experimentsestablished two independent branch pathways from matairesinol; one giving rise to yatein and the other tobursehernin [1].Next, the author expanded the quantitation system to the cinnamate/monolignol pathway, because, inthe post-genomic era, much attention has been focused on the overall understanding of the integratedcontrol mechanisms for the pathway in relation to xylem formation.Again, the author synthesized deuterium-labeled and unlabeled standards for all the compounds on thepathway, and established a comprehensive metabolite quantitation system for the pathway. Using thesystem and that for lignan biosynthesis established previously [1], the author measured comprehensivelythe amounts of the metabolites on the cinnamate/monolignol and lignan pathways in the C. tinctorius cv.24~ ABSTRACTS (PH D FOR GRADUATE SCHOOL OF AGRICULTURE)Round-leaved White seeds. In addition, the author carried out the simultaneous administration of twodistinctly-labeled compounds to the seeds. Taken together, the results of these experiments suggestedstrongly the intermediacy of ferulic acid in lignan biosynthesis in C. tinctorius seeds. This is in sharpcontrast to the current view of lignin biosynthesis that ferulic acid is not involved in lignin biosynthesis as aprecursor [4].In conclusion, the present study established for the first time the precise and comprehensivemetabolite quantitation (metabolic profiling) systems for the cinnamate/monolignol and lignan pathways bythe use of a stable-isotope-dilution method. The system was successfully applied to the metabolic analysisof lignan pathway in Anthriscus sylvestris, and the pathway from matairesinol to yatein was established. Inaddition, the intermediacy of ferulic acid in lignan biosynthesis in Carthamus tinctorius cv. Round-leavedWhite was strongly suggested. The quantitation systems would be useful tools for elucidating integratedmechanisms for xylem formation in trees.REFERENCES[1] N. Sakakibara, S. Suzuki, T. Umezawa and M. Shimada, Org. Biomol. Chem., 2003,1,2474.[2] N. Sakakibara, T. Umezawa and M. Shimada, Proceedings of the 41" Lignin Symposium, 2002, pp.112.[3] T. Umezawa, Phytochemistry Reviews, 2003,2, 37l.[4] L. Li, J. L. Popko, T. Umezawa and V. L. Chiang,J. Biol. Chem., 2000, 275, 6537.25

Metabolic Analysis of the Cinnamate/Monolignol and Lignan Pathways(ABSTRACTS (PH D FOR GRADUATE SCHOOL OF AGRICULTURE))

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Metabolic Analysis of the Cinnamate/Monolignol and Lignan Pathways(ABSTRACTS (PH D FOR GRADUATE SCHOOL OF AGRICULTURE))

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