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dc.contributor.authorSalim, Vonny
dc.date.accessioned2013-08-23T13:03:30Z
dc.date.available2014-08-19T09:00:04Z
dc.date.issued2013-08-23
dc.identifier.urihttp://hdl.handle.net/10464/4934
dc.description.abstractThe monoterpenoid indole alkaloids (MIAs) of Madagascar periwinkle (Catharanthus roseus) are known to be among the most important source of natural drugs used in various cancer chemotherapies. MIAs are derived by combining the iridoid secologanin with tryptamine to form the central precursor strictosidine that is then converted to most known MIAs, such as catharanthine and vindoline that dimerize to form anticancer vinblastine and vincristine. While their assembly is still poorly understood, the complex multistep pathways involved occur in several specialized cell types within leaves that are regulated by developmental and environmental cues. The organization of MIA pathways is also coupled to secretory mechanisms that allow the accumulation of catharanthine in the waxy leaf surface, separated from vindoline found within leaf cells. While the spatial separation of catharanthine and vindoline provides an explanation for the low levels of dimeric MIAs found in the plants, the secretion of catharanthine to the leaf surface is shown to be part of plant defense mechanisms against fungal infection and insect herbivores. The transcriptomic databases of Catharanthus roseus and various MIA producing plants are facilitating bioinformatic approaches to identify novel MIA biosynthetic genes. Virus-induced gene silencing (VIGS) is being used to screen these candidate genes for their involvement in iridoid biosynthesis pathway, especially in the identification of 7-deoxyloganic acid 7-hydroxylase (CrDL7H) shown by the accumulation of its substrate, 7-deoxyloganic acid and decreased level of secologanin along with catharanthine and vindoline. VIGS can also confirm the biochemical function of genes being identified, such as in the glucosylation of 7-deoxyloganetic acid by CrUGT8 shown by decreased level of secologanin and MIAs within silenced plants. Silencing of other iridoid biosynthetic genes, loganic acid O-methyltransferase (LAMT) and secologanin synthase (SLS) also confirm the metabolic route for iridoid biosynthesis in planta through 7-deoxyloganic acid, loganic acid, and loganin intermediates. This route is validated by high substrate specificity of CrUGT8 for 7-deoxyloganetic acid and CrDL7H for 7-deoxyloganic acid. Further localization studies of CrUGT8 and CrDL7H also show that these genes are preferentially expressed within Catharanthus leaves rather than in epidermal cells where the last two steps of secologanin biosynthesis occur.en_US
dc.language.isoengen_US
dc.publisherBrock Universityen_US
dc.subjectmonoterpenoid indole alkaloiden_US
dc.subjectiridoiden_US
dc.subjectbiosynthetic genesen_US
dc.subjectplant secondary metabolismen_US
dc.subjectCatharanthus roseusen_US
dc.titleFunctional Characterization of Monoterpenoid Indole Alkaloid (MIA) Biosynthetic Genes in Catharanthus roseusen_US
dc.typeElectronic Thesis or Dissertationen_US
dc.degree.namePh.D. Biotechnologyen_US
dc.degree.levelDoctoralen_US
dc.contributor.departmentCentre for Biotechnologyen_US
dc.degree.disciplineFaculty of Mathematics and Scienceen_US
dc.embargo.terms12 Monthsen_US
refterms.dateFOA2021-08-08T02:03:04Z


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