Changes of taxane production and gene expression during the development of in vitro Taxus plant cultures

The production and accumulation of secondary metabolites in plants is always regulated by the expression of genes involved in their biosynthesis. There are very few reports about the regulation of the biosynthesis of the anticancer agent taxol and other related taxanes and the rate-limiting steps involved, especially during the development of Taxus plants. Using Taxus baccata L. plantlets grown in vitro for 1 year, our group has studied the relationship between the profile and production of taxanes and the expression of genes codifying for enzymes that participate in early and late steps of taxane biosynthesis ( TXS , DBAT , BAPT and DBTNBT ). A far higher taxane content was observed in the aerial part of the plantlets than in the roots, 10-deacetylbaccatin III being the most abundant taxane, with very low conversion to baccatin III and taxol. The mRNA accumulation of the studied genes was also higher in the aerial part than in the corresponding roots. Our results indicate that the low taxane levels in the roots could reflect the low transcript accumulation of the aforementioned genes in this part of the plant, although an active metabolism or translocation of taxanes to the aerial part could also be responsible. The high content of 10-deacetylbaccatin III and very low levels of baccatin III, together with the low mRNA accumulation of DBAT in the aerial part, suggest that this gene could control a limiting step in the taxane biosynthetic pathway in T. baccata plantlets grown for 1 year in in vitro conditions.