Transcriptional repression of terpenoid indole alkaloid biosynthesis in Catharanthus roseus

Abstract

Catharanthus roseus is the only commercial source for vincristine, which is commonly used for the treatment of several cancers, but its supply is insufficient. Vincristine is a terpene indole alkaloid (TIA) and TIAs are produced at very low levels in C. roseus. Understanding the regulation of TIA biosynthesis is required to engineer a plant system with increased TIA accumulation. These engineered systems would enable a more reliable and cost-efficient way to provide vincristine. Overexpression of activators has resulted in limited increases in TIAs and therefore, understanding the role of repressors might be key to increasing TIA contents in C. roseus. In this thesis, I evaluate or identify the role of two classes of repressors in C. roseus: zinc finger Catharanthus transcription factors (ZCT) and Jasmonate-Associated MYC-like (JAM) transcription factors. Here I describe a transient transformation method for C. roseus which allows overexpression of genes of interest and therefore the rapid screening of candidate genes (Chapter 1). I have used this method and further techniques to study the regulation of ZCT1, a repressor of the TIA pathway (Chapter 2). Furthermore, I have identified two new repressors of the TIA pathway, CrJAM2 and CrJAM3, and investigated their function in C. roseus (Chapter 3). The transient transformation method is a valuable tool for the C. roseus community to study gene function, including genes involved in TIA biosynthesis and its regulation. Insights into the function of ZCT1, CrJAM2, and CrJAM3 will hopefully aid in the development of a plant system with increased TIA accumulation to provide a more reliable and cost-efficient way to produce vincristine.--Author's abstract