Browsing by Author "Smit, Jacobus Samuel"

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    Sequence-function relationships of the Vitis vinifera L. terpene synthase (VviTPS) family towards understanding the grapevine flower volatilome
    (Stellenbosch : Stellenbosch University, 2020-04) Smit, Jacobus Samuel; Young, Philip R.; Vivier, Melane A.; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.
    ENGLISH ABSTRACT: Terpenes are ubiquitous to plants and represent the most diverse class of natural products. More than 50 000 terpenes have been described in nature with the enzymes involved in their biosynthesis, namely terpene synthases (TPS), facilitating some of the most complex catalytic activities observed in nature. Terpenes are hydrocarbons that are made of five carbon building blocks. The coupling and prenylation of these building blocks result in different substrates that are characteristic to the biochemical properties of the synthesised terpene. The C10 monoterpene and C15 sesquiterpene compounds are extensively studied due to their volatility. These terpene classes are often associated with the pleasant aromas emitted by flowers, fulfilling important roles as volatile attractants. Terpenes are also known to have strong antimicrobial and insecticidal activities. These metabolites are important defence compounds and are therefore also considered to be specialised metabolites due to the fitness advantage associated with their ecophysiological activities. Grapevine, Vitis vinifera L. (Vitaceae), has one of the largest TPS families, with the majority of these genes involved in mono- and sesquiterpene biosynthesis. These terpene classes are extensively studied for their organoleptic properties in grapes and wine, most often associated with aromatic wines that have floral, Muscat or pepper aromas. The genetic potential of grapevine TPS genes is largely underappreciated seeing that most studies focus on a select few terpene classes that are relevant to wine flavour and aroma. Limited studies have provided some insight into the in planta emission of grapevine terpenes. Grapevine flowers have been identified is a promising organ for terpene biosynthesis due to extensive upregulation of the TPS genes and a concomitant emission of volatile terpenes. Grapevine flowers were therefore characterised for their volatile profiles to identify chemotypic differences. This resulted in the identification of unique chemotypes, with cultivar-specific major sesquiterpene volatiles observed. The genetic factors that contribute to the volatile differences were analysed through functional and computational characterisation. This resulted in functional characterisation of numerous sesquiterpene synthases with aberrant mutations rendering more than half of the isolated genes non-functional. Furthermore, a novel sesquiterpene synthase involved in the unique chemotype of the cultivar Muscat of Alexandria was characterised. This enzyme showed a unique enzyme active site that was linked to the biosynthesis of (E)-β-farnesene. In addition to functional characterisation of genes was the annotation and computational characterisation of the TPS gene families for three diploid grapevine genomes. This allowed for new and fundamentally important insight into how this gene family differs between genotypes. The TPS gene family of grapevine is of great importance from an ecophysiological and economic perspective. By studying the genetic and chemotypic variations in multiple genotypes it was possible to characterise the grapevine TPS landscape. The insights gained from this study provided important fundamental knowledge that furthers our understanding of the complex biochemical and genetic processes involved in grapevine terpene biosynthesis.