Characterization and Utilization of the Factors that Regulate Production of Metabolites and Phytomedicines

In plants, a number of transcription factors (TFs) have been shown to act as key regulators of various functions in plants. Therefore, modification of transcription factors is an effective strategy for manipulation of plant traits, which include alternation of morphology, metabolite pathway. It becomes evident, however, that ectopic expression or gene knockout of the gene for TF is not very effective for the manipulation of plant traits, mainly due to gene redundancy. To overcome such difficulty, we developed novel gene silencing system using a transcriptional repressor, named CRES-T, in which a transcription factor is converted into a strong repressor (a chimeric repressor) by fusion with SRDX, a EAR-like-motif repression domain from SUPERMAN, and suppress the target genes dominantly over the endogenous and functionally redundant factors, resulted in the induction of phenotype similar to loss-of-function of the transcription factor gene. Using CRES-T system, we are identifying TFs that regulate morphology and metabolic pathway in Arabidopsis and Oryza sativa. We identified that the expression of a chimeric repressor, designated HR2751, against a bHLH transcription factor of which expression is correlated with an enzymatic gene involved in tryptophan pathway, resulted in accumulation of an excess amount of glucosinolates. In addition, we have identified chimeric repressors that increased biomass of Oryza sativa and that alter morphology of a medical plant, Coptis japonica, suitable for cultivation in greenhouse without loosing productive activity of alkaloid. We present possible strategy for the manipulation of plant traits using chimeric repressors.