Genome and transcriptome guided gene discovery in plant secondary metabolism

• Main Author: Kellner, Franziska
• Published: University of East Anglia 2016
• Subjects: 581.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709776

Plants produce a wide range of complex secondary metabolites that have many applications, for example as pharmaceutical agents. Gene discovery and the elucidation of these unique biosynthetic pathways is challenging since many of the enzymatic transformations are unprecedented. In Catharanthus roseus, the sole producer of the valuable anti-cancer compounds vinblastine and vincristine, the biosynthetic pathway for these alkaloids is highly complex and crucial steps are still unknown. Recently, the tight transcriptional co-regulation of the early part of this pathway enabled discovery of some of the central enzymatic steps by analysing the gene co-expression patterns and testing potential candidates using virus induced gene silencing. Additionally, it has become apparent that some plant secondary metabolite pathways exhibit physical clustering of pathway related genes in the genome. This thesis highlights how both strategies of gene discovery can be applied for the targeted discovery of genes for missing steps in biosynthesis of non-model plants. Co-expression analysis to identify candidates and subsequent testing of these candidates using virus induced gene silencing has led to the discovery and subsequent characterisation of the enzyme tabersonine 3-oxygenase (T3O), a key oxidation step in vindoline biosynthesis. This thesis furthermore reports the first C. roseus whole genome sequence. Additionally a BAC library was obtained and selected BACs sequenced. Analysis of the combined sequencing data established that gene clustering does indeed occur for alkaloid biosynthesis in C. roseus and yielded a new set of candidates for so far unknown pathway enzymes. Selected candidates have been tested by silencing or expression and results are discussed. The sequence information provides a valuable resource for the wider community, available as a searchable, publically available database (http://medicinalplantgenomics.msu.edu/). The work presented in this thesis highlights how next generation sequence data can be exploited to elucidate complex secondary metabolic pathways.