Contribution of taxane biosynthetic pathway gene expression to observed variability in paclitaxel accumulation in Taxus suspension cultures

Variability in product accumulation is one of the major obstacles limiting the widespread commercialization of plant cell culture technology to supply natural product pharmaceuticals. Despite extensive process engineering efforts, which have led to increased yields, plant cells exhibit variability in productivity that is poorly understood. Elicitation of Taxus cultures with methyl jasmonate (MeJA) induces paclitaxel accumulation, but to varying extents in different cultures. In the current study, cultures with different aggregation profiles were established to create predictable differences in paclitaxel accumulation upon MeJA elicitation. Expression of known paclitaxel biosynthetic genes in MeJA-elicited cultures exhibiting both substantial (15-fold) and moderate (2-fold) differences in paclitaxel accumulation was analyzed using quantitative reverse transcriptase PCR. Each population exhibited the characteristic large increase in paclitaxel pathway gene expression following MeJA elicitation; however, differences in expression between populations were minor, and only observed for the cultures with the 15-fold variation in paclitaxel content. These data suggest that although upregulation of biosynthetic pathway gene expression contributes to observed increases in paclitaxel synthesis upon elicitation with MeJA, there are additional factors that need to be uncovered before paclitaxel productivity can be fully optimized.