Bupleurum kaoi, an important medicinal plant endemic to Taiwan, contains various phytosterols and bioactive triterpene saikosaponins. Saikosaponins have been reported to have pharmacological properties such as anti-allergic, anti-inflammatory, anti-hepatotoxic, and also for lowering fever. However, the understanding of the molecular aspects of the metabolic pathways of the plant and its responses to adverse environmental factors is relatively rudimentary. There are only a few studies for the plant regeneration and genetic transformation on Bupleurum plants. This study contains two parts: the first part is the functional characterization of the ethylene response factors. The second part is the development of a protocol for the Agrobaterium tumefaciens-mediated transformation in B. kaoi.
In nature, plants are challenged by various biotic and abiotic stresses including microorganisms and insects attack as well as temperatural and hormonal effects, which lead to an array of defensive countermeasures that involve the activation of highly regulated signal transduction pathways which trigger rapid defense responses in plant cells. In a previous report from our laboratory, the exogenous application of methyl jasmonate (MeJA) increased saikosaponin production and induced transcriptional changes in adventitious root cultures of B. kaoi. In this research, three novel ethylene response factor (ERF) genes were isolated from B. kaoi and the function of their gene products was characterized. Northern blots analyses were applied to monitor the expression levels of BkERFs transcripts in mature B. kaoi plants and in response to plant hormone applications. BkERFs were localized in the plant nucleus and functioned as transcriptional activators when transiently expressed in B. kaoi cells. Transgenic B. kaoi cells and Arabidopsis thaliana plants overexpressing BKERFs resulted in elevated mRNA levels of the defense genes, and enhanced resistance to Botrytis. cinerea. The results provide evidence that BkERFs mediate the expression of defense-related genes in plants.
Genetic transformation provides means for studying the function of a targeted gene using the homologously or heterologously transformed plants. In second part of this study, a method using B. kaoi cells with Agrobacterium tumefaciens mediated transformation and regeneration was developed. It provides a powerful tool to study the function of genes in B. kaoi.

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