TRANSCRIPTIONAL AND POST-TRANSLATIONAL REGULATION OF TERPENOID INDOLE ALKALOID BIOSYNTHESIS IN CATHARANTHUS ROSEUS

• Main Author: Paul, Priyanka
• Format: Text
• Language: unknown
• Published: UKnowledge 2017
• Subjects: AP2/ERF gene cluster; Catharanthus roseus; MAP kinome; terpenoid indole alkaloids; transcriptional and post-translational regulation; Biotechnology; Physiology; Plant Biology; Orca
• Online Access: https://uknowledge.uky.edu/pss_etds/94; https://doi.org/10.13023/ETD.2017.403; https://uknowledge.uky.edu/context/pss_etds/article/1101/viewcontent/Paul_Priyanka_Dissertaion.pdf

Catharanthus roseus (Madagascar periwinkle) is the exclusive source of an array of terpenoid indole alkaloids (TIAs) that are used in the treatments of hypertension and certain types of cancer. TIA biosynthesis is under stringent spatiotemporal control and is induced by jasmonate (JA) and fungal elicitors. Tryptamine, derived from the indole branch, and secologanin from the iridoid branch are condensed to form the first TIA, strictosidine. Biosynthesis of TIA is regulated at the transcriptional level and several transcription factors (TFs) regulating the expression of genes encoding key enzymes in the pathway have been isolated and characterized. The JA-responsive APETALA2/ETHYLENE RESPONSE FACTOR (AP2/ERF), ORCA3, and the basic helix-loop-helix (bHLH) factor, CrMYC2, are the key activators of the TIA biosynthesis. Recently, two other TFs, the bHLH IRIDOID SYNTHESIS 1 (BIS1) and BIS2 were also identified as regulators of TIA pathway. Analysis of C. roseus genome sequence has revealed that ORCA3 forms a physical cluster with two uncharacterized AP2/ERFs, ORCA4 and ORCA5. In plants, physically linked clusters of TFs are less characterized. Moreover, the regulation of TF clusters is relatively unexplored. My research uncovered that the ORCA gene cluster is differentially regulated. ORCA4 and ORCA5, while functionally overlapping with ORCA3, regulate an additional set of TIA pathway genes. ORCA4 or ORCA5 overexpression has resulted in significant increase of TIA accumulation in C. roseus hairy roots. In addition, ORCA5 directly regulates the expression of ORCA4 and indirectly regulates ORCA3, likely via unknown factor(s). Interestingly, ORCA5 also activates the expression of ZCT3, a negative regulator of the TIA pathway. In addition CrMYC2 is capable of activating ORCA3 and co-regulating pathway genes concomitantly with ORCA3. Several lines of evidence suggest that, in addition to the transcriptional control, biosynthesis of TIAs is also controlled at the posttranslational level, such as protein phosphorylation. ...