Transcriptional response of the terpenoid indole alkaloid pathway to the overexpression of ORCA3 along with jasmonic acid elicitation of Catharanthus roseus hairy roots over time.

Jasmonic acid (JA) activates the transcriptional regulator ORCA3, which has a role in regulating the terpenoid indole alkaloid (TIA) pathway within Catharanthus roseus. The TIA pathway leads to the production of the anticancer drugs vinblastine and vincristine. This work explores the transient effects of overexpressing ORCA3 under the control of a glucocorticoid-inducible promoter system in C. roseus hairy roots along with the simultaneous feeding of JA. The changes in TIA metabolites and in mRNA transcripts of pathway genes and regulators were tracked for 72h. Upon induction of ORCA3 expression and elicitation with JA, ORCA3 transcripts increased 170-fold whereas ORCA3 expression caused an 89-fold increase and JA elicitation caused a 5-fold increase in ORCA3 transcripts. JA treatment caused the largest increase in TIA metabolites and transcripts of pathway genes. These transcripts displayed a transient response with the maximum expression reached between 12 and 24h. In the samples overexpressing ORCA3, the largest increase in the transcripts of ZCT1 and ZCT2 (ZCT-zinc finger-binding protein), TIA transcriptional repressors, coincided with the largest increase in ORCA3 transcripts. This counter response of transcriptional repressors may explain why the large increase in ORCA3 transcripts do not correspond with larger increases in transcripts of TIA pathway genes.