| Research Abstract |
Heartwood is the colored region of the inner part of free trunks, and its formation is a metabolic event specific to woody plants, as it does not operate in herbaceous plants. Recently, metabolic engineering of trees has been developed significantly. For example, a transgenic aspen (Populus tremuloides) with less lignin and higher cellulose contents has been successfully produced by Chiang and co-workers (Hu, et. al., 1999 ; Li, et. al., 2003). These developments were achieved with the aid of the knowledge of herbaceous plant molecular biology. Now, it is necessary to exploit knowledge of molecular mechanisms for metabolic events specific to woody plants in order to accelerate metabolic engineering of trees. Although nothing is known about the molecular mechanisms, the facts that biosynthesis of lignans, norlignans and related compounds are involved in heartwood formation implies that the molecular mechanisms of their biosynthesis can be a clue to help us elucidate heartwood formation
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mechanisms.
Since in 1990 Umezawa, et. al. reported the first enzymatic reaction producing an optically pure lignan from achiral coniferyl alcohol (Umezawa, et. al. 1990), much has been learned about the enzymes synthesizing lignans (Umezawa, 2001 ; Umezawa, 2003 ; Umezawa, 2005 ; Suzuki and Umezawa, 2007). In addition, a norlignan synthase activitie has been detected (Suzuki, et. al., 2002). In the present project as the continuation of the previous works, the principal investigator (Umezawa) and the co-workers have investigated the biosynthetic mechanisms of lignans and norlignans. Thus, they first established a system for comprehensive quantitative analysis of the cinnamate/monolignol pathway compounds which are precursors of lignans, norlignan, and lignins. Then, the molecular mechanisms of lignan biosynthesis and norlignan biosynthesis were studied. In addition, the genes encoding some enzymes of the cinnamate/monolignol pathway which is the upstream step of lignan, norlignan and lignin biosyntheses were also characterized. Less
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