Abstract
BackgroundPlant cell culture represents an alternative source for producing high-value secondary metabolites including paclitaxel (Taxol®), which is mainly produced in Taxus and has been widely used in cancer chemotherapy. The phytohormone methyl jasmonate (MeJA) can significantly increase the production of paclitaxel, which is induced in plants as a secondary metabolite possibly in defense against herbivores and pathogens. In cell culture, MeJA also elicits the accumulation of paclitaxel; however, the mechanism is still largely unknown.Methodology/Principal FindingsTo obtain insight into the global regulation mechanism of MeJA in the steady state of paclitaxel production (7 days after MeJA addition), especially on paclitaxel biosynthesis, we sequenced the transcriptomes of MeJA-treated and untreated Taxus × media cells and obtained ∼ 32.5 M high quality reads, from which 40,348 unique sequences were obtained by de novo assembly. Expression level analysis indicated that a large number of genes were associated with transcriptional regulation, DNA and histone modification, and MeJA signaling network. All the 29 known genes involved in the biosynthesis of terpenoid backbone and paclitaxel were found with 18 genes showing increased transcript abundance following elicitation of MeJA. The significantly up-regulated changes of 9 genes in paclitaxel biosynthesis were validated by qRT-PCR assays. According to the expression changes and the previously proposed enzyme functions, multiple candidates for the unknown steps in paclitaxel biosynthesis were identified. We also found some genes putatively involved in the transport and degradation of paclitaxel. Potential target prediction of miRNAs indicated that miRNAs may play an important role in the gene expression regulation following the elicitation of MeJA.Conclusions/SignificanceOur results shed new light on the global regulation mechanism by which MeJA regulates the physiology of Taxus cells and is helpful to understand how MeJA elicits other plant species besides Taxus.
Highlights
Taxus, known as yew, is a genus of gymnosperm and contains at least 14 species [1]
Because the paclitaxel biosynthesis pathway is incomplete in the kyoto encyclopedia of genes and genomes (KEGG) database, to find the genes responsible for the biosynthesis of the main chain of terpenoid backbone, we manually identified all genes involved in these two pathways by reciprocal BLAST search against the transcriptome using previous reported enzymes as queries (Table S8)
In an effort towards establishing high paclitaxel producing cell cultures, the plant hormone methyl jasmonate (MeJA) was used to elicit the accumulation of paclitaxel
Summary
Known as yew, is a genus of gymnosperm and contains at least 14 species [1]. Great efforts have been taken to increase the production of paclitaxel by finding alternative sources and methods of synthesis including Taxus needles [4,5] fungal sources [4,5], developing semisynthesis method from related taxanes [6], and using plant cell cultures [7]. Due to the high demand, a combined method of production is mostly used in which an abundant natural intermediate metabolite compound is isolated from natural sources (yew bark and needle) or by plant cell culture, and using semisynthesis methods to obtain paclitaxel. Plant cell culture represents an alternative source for producing high-value secondary metabolites including paclitaxel (TaxolH), which is mainly produced in Taxus and has been widely used in cancer chemotherapy. MeJA elicits the accumulation of paclitaxel; the mechanism is still largely unknown
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