| Summary: | Operon-like gene clusters are functional cassettes of physically linked and non-homologous genes involved in the same pathway. To date, 20 such plant gene clusters have been discovered, all of which are involved in specialised metabolism. Plant gene clusters raise interesting biological questions about their importance and the drivers behind their formation. This thesis describes the investigation of the evolution of the avenacin gene cluster, discovered in the diploid oat Avena strigosa S75, via wet-bench experiments and bioinformatic analyses, commencing with the general introduction (Chapter 1). Chapter 2 to 4 describe the survey on the avenacin production, expression pattern and phylogeny of the �ve characterized avenacin biosynthetic (Sad) genes within Aveninae, focusing on Avena L. The genomes of all Avena spp. investigated, including the avenacin de�cient A. longiglumis, possess the �ve Sad gene homologues. The expression pattern of the Sad gene homolgoues vary in a genome-type dependent manner that it is root-speci�c amongst A genome oats. However, the C genome oats show root and leaf expressions, contributed by di�erentially expressed Sad gene duplicates. Chapter 5 and 6 describe the molecular evolutionary analysis of the �ve gene families implicated in triterpene biosynthesis: oxidosqualene cyclases, cytochromes P450 51s, Clade 1A serine carboxypeptidase-like acyltransferases, Class I O-methyl transferases and Group L glycosyltransferases in monocots. Phylogenetics analyses show that these gene families evolve via duplication-neofunctionalisation, facilitated by gene GC content and exon-intron structures changes under purifying selection on amino acid sequences. Syntenic study of the triterpene biosynthetic gene families reveals the ancestral triterpene biosynthetic OSC/CYP51 gene pair found in the �-WGD event. Finally, the evolutionary model of the avenacin biosynthesis and the potential applications of the knowledge of gene clustering in systematic and synthetic biology are descibed in Chapter 7.
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