School of Botany - Theses

Permanent URI for this collection

Search Results

Now showing 1 - 10 of 182
  • Item
    Thumbnail Image
    A systematic revision of the Harpetidae (Trilobita) and a critique of cladistic biogeographic methodology
    Ebach, Malte C. (University of Melbourne, 2002)
    The ten genera of Harpetidae (Bohemoharpes, Brachyhipposiderus, Dolichoharpes, Dubhglasina, Eoharpes, Harpes, Kielania, Lioharpes, Scotoharpes and gen. nov.) are reviewed. The monophyly of the Harpetidae is corroborated, and all ingroup genera can be defended as monophyletic groups except for the non-monophyletic Scotoharpes group. Emended diagnoses are provided for all the genera within the family. The three subfamilies Dolichoharpinae, Eoharpetinae and Harpetinae are placed in synonymy within the Harpetidae. The genera Australoharpes and Sinoharpes are placed in synonymy with Dubhglasina. Thorslundops and Wegelinia are placed in synonymy with Hibbertia, and the subgenus Lioharpes (Fritchaspis) placed in synonymy with Lioharpes. Four new species of Kielania (Kielania spp. 1-4) and a new genus (gen. nov.) and two new species (gen. nov. spp. 1-2) are described for the first time. Using these eight harpetid genera (Bohemoharpes, Dubhglasina, Eoharpes, Harpes, Hibbertia, Kielania, Lioharpes and Scotoharpes), the cladistic methods of standard parsimony and three-item analysis are compared. The methodological integrity of these methods is thoroughly examined and their inner workings exposed. Many cladists today use these programs without investigating how the black box of algorithms functions or the implications of the process they apply to the input data. Three-item analysis emerges as the more rigorous method, satisfying the discovery paradigm. Several cladograms based on three-item analysis that specify monophyletic taxa from the Siluro- Ordovician are transformed to taxon-area cladograms and combined to uncover geographic congruence. Cladistic biogeography uncovers geographic congruence using cladistic-based methodologies. The agreement of several taxon-area cladograms rarely yields a fully resolved result. Areas may overlap, taxa may not be evenly distributed and thus, ambiguity may be prevalent in the data. Ambiguity is incongruence and may be resolved by reducing paralogy and resolving potential information. During the last 20 years, several new approaches in cladistic biogeography (i.e. Brooks Parsimony Analysis, Assumption 0) have interpreted ambiguity as congruence. These methods are problematic because they are generational. Methods constructed under the generation paradigm are qualifiers for flawed concepts and immunize such concepts from falsifying evidence. A critique of modified Brooks Parsimony Analysis (BPA) reveals that taking an a priori evolutionary stance in biogeography leads to flaws in implementation. Area cladistics adopts paralogy-free sub-tree analysis, using Assumption 2, to discover the relative positions of continents through time. Geographic congruence is best explained by allopatry (geographic isolation). Vicariance, dispersal and combinations of both are recognized causes for allopatric speciation. Area cladistics highlights the concept that all these events occur in response to geological changes (e.g. continental drift) either directly, by geographic boundaries, or indirectly, at the level of ocean currents. Examples from the literature and from the harpetid genus Hibbertia all agree with the geological process. The examples include Ordovician-Silurian and Lower Devonian trilobites to yield a general areagram, which is a representational branching diagram that depicts the relationships of areas. Finding one common biogeographic pattern from several unrelated groups is a qualitative approach to interpret the positions of continental margins through time. Area cladistics is not a substitute for palaeomaps that are derived from palaeomagnetic data, but general areagrams add to the body of knowledge and yield more precise interpretations of the Earth's past.
  • Item
    Thumbnail Image
    Characterisation of cyanogenic glucoside synthesis in Eucalyptus
    Neilson, Elizabeth H. (University of Melbourne, 2012)
    Cyanogenic glycosides are nitrogen-containing defensive metabolites, releasing toxic hydrogen cyanide following tissue disruption and contact with catabolic enzymes. Within the ecologically and commercially important genus Eucalyptus, approximately 4% of species are cyanogenic, possessing the phenylalanine-derived cyanogenic glucoside prunasin. Cyanogenic Eucalyptus species have been identified as an excellent experimental system in which to investigate defensive ontogenetic regulation as different species have shown variability in the onset and regulation of cyanogenic glucoside biosynthesis through plant development. The overall aim of this PhD thesis is to characterise cyanogenic glucoside synthesis in cyanogenic Eucalytpus species throughout leaf and plant ontogeny by investigating the synthesis, turnover and regulation of cyanogenic glucoside/(s) in E. yarraensis and E. camphora. Using various PCR techniques, four cytochrome P450 genes encoding CYP79 enzymes were detected and isolated from E. yarraensis: CYP79A34, CYP79A35, CYP79A36 and CYP79A37. The CYP79A34 gene was functionally cloned and expressed in Saccharomyces cerevisiae using the USER� cloning technique and a modified pYeDP60 vector, respectively. The recombinantly expressed CYP79A34 was shown to catalyze the conversion of L- phenylalanine into phenylacetaldoxime, verifying its involvement in the first step of prunasin biosynthesis. Using quantitative real-time PCR, CYP79A34 mRNA levels were found to be positively correlated with an increase in prunasin concentration during E. yarraensis ontogeny, suggesting that prunasin synthesis is regulated at the transcript level. Interestingly, CYP79A34 transcript levels also significantly increased in leaves subject to cold temperature and nitrogen application. To further investigate how leaf ontogeny affects the synthesis and possible turnover of prunasin, E. yarraensis coppice branches were pulse-labeled with 14C (via 14C02) and the incorporation of 14C into the nitrile constituent of the cyanogenic glucoside was measured in individual leaves over a 72 h period. Despite the high similarity observed in physical parameters and overall patterns of prunasin allocation across different leaf classes, a surprisingly high level of variability in 14C incorporation was encountered. Prunasin synthesis and turnover was observed in both expanding and fully expanded E. yarraensis leaves, although an accurate measure of turnover was not achieved. Interestingly, diurnal variation in specific activity suggests that the synthesis of prunasin may be influenced by light-dependent plant processes. Whole plant ontogenetic effects on cyanogenic glucoside synthesis were investigated in E. camphora, by identifying, tracking and comparing the concentration and composition of multiple cyanogenic glucosides throughout different ontogenetic stages. Using different analytical methods (LC-MS/MS, GC-MS and NMR) six phenylalanine-derived cyanogenic glucosides were identified, including three cyanogenic diglucosides characterised by unique linkage positions between the two glucose moieties. Two of these cyanogenic glucosides have not previously been reported and were named eucalyptosin B and eucalyptosin C. Interestingly, the different cyanogenic diglucosides could be distinguished by unique MS/MS fragmentation patterns. This knowledge should facilitate analysis and structural elucidation of cyanogenic diglucosides from other plant species. Quantitative and qualitative differences in total cyanogenic glucoside content were observed across different stages of whole plant and tissue ontogeny, as well as within different tissue types. Seedlings of E. camphora were found to produce only the cyanogenic monoglucoside prunasin, but "switch on" prunasin biosynthesis at different times. Once initiated, total cyanogenic glucoside concentration increased throughout plant ontogeny with cyanogenic diglucoside production initiated in saplings and reaching a maximum in flower buds of adult trees. Overall this work uncovered many novel aspects of cyanogenic glucoside synthesis in E. camphora and E. yarraensis, particularly in terms of ontogenetic regulation, and provides a solid platform to further investigate these species and their unique control over cyanogenic glucoside synthesis.
  • Item
    Thumbnail Image
    Grape and botrytis cinerea proteases : characterization and utilization in winemaking
    Van Sluyter, Steven C (University of Melbourne, 2012)
    Grape berries contain high levels of pathogenesis-related (PR) proteins that persist through winemaking and cause commercially unacceptable heat-induced hazes if not removed before bottling. Nearly every commercial winery uses the clay cation exchanger bentonite to remove PR-proteins from wine, but the process results in wine losses, is laborious, and can negatively affect wine sensory properties. An alternative to protein removal by bentonite is hydrolysis of PR-proteins by proteases. However, PR-proteins are highly resistant to enzymatic proteolysis and no commercially viable enzymatic method has been discovered in at least 60 years of attempts. The purpose of the research presented in this thesis was to discover grape and Botrytis cinerea enzymes that could be utilized during winemaking to reduce or eliminate the need for bentonite by degrading PR?proteins. Grapes infected with B. cinerea have been observed previously to have lower levels of PR?proteins than healthy grapes or grapes infected with other pathogens. To investigate Botrytis proteases, knock-out mutants were screened on grape berries and against purified PR-proteins on agar plates. The mutants were no more inhibited by PR?proteins than the wild type, suggesting that either the aspartic proteases serve redundant functions, or their function in vivo is unrelated to grape PR-proteins. A Botrytis protease previously found to be the most highly secreted protein in liquid culture was heterologously produced in Pichia pastoris and used in winemaking trials. The Botrytis protease, BcAP8, significantly reduced the PR-proteins most prone to aggregation, chitinases, but did not significantly reduce,thaumatin?like proteins. BcAP8 could be an effective treatment for reducing bentonite in wines with unstable,chitinases. Using activity-based probes to enrich for proteases followed by mass spectrometry, grape papain-like cysteine proteases were characterized for the first time. One of the proteases is highly glycosylated, contains an extra disulfide bond and several other novel sequence features, and represents a new sub?family of plant proteases. Serine and nepenthesin?like aspartic grape proteases were also discovered by mass spectrometry. The cysteine protease activity of grape berries, most likely attributable to the newly discovered highly glycosylated protease, was associated with the insoluble material of grape juice and was highly heat stable. Those two attributes were exploited to develop a flash pasteurization method that effectively eliminated the need for bentonite in the tested juices.
  • Item
    No Preview Available
    Evaluating the ecological and operational basis of vegetation condition assessments
    Gorrod, EmMA (University of Melbourne, 2011)
    Globally, market based policies for biodiversity conservation are emerging that aim to achieve better and more cost efficient biodiversity outcomes than traditional command and control mechanisms. Investment accounting, reverse auctions and biodiversity offsets aim to achieve No Net Loss or Net Gain of biodiversity by incorporating biodiversity into the financial decisions of landholders. Market based policies require a proxy commodity for biodiversity that numerically express the capacity of a given site to support biodiversity, and Australia has pioneered the development of vegetation condition indices for this purpose. For every market based decision, there is a chance that the actual biodiversity outcome will be better or worse than expected. Risks of worse than expected outcomes may have significant financial implications and irreversible repercussions for biodiversity. Uncertainty in estimates of current and future vegetation condition may increase these risks. Despite this, market based policies have not been developed within a risk management framework and no systematic analysis of factors that may contribute to uncertainty in biodiversity valuation has previously been conducted. This thesis evaluates the nature of uncertainties in the ecological and operational basis of vegetation condition assessments, and considers the potential effects of uncertainty on the biodiversity outcomes of market based policies. Chapter 2 proposes a framework for identifying epistemic and linguistic uncertainties in current and predicted future estimates of vegetation condition. It contends that uncertainty may arise due to: i) conceptual uncertainty about the factors and processes that are causally related to the definition of biodiversity value; ii) quantitative uncertainty concerning misrepresentation of causal factors and processes by the mathematical constructs of the index; and iii) data uncertainty arising from errors in the input data. Specific occurrences of these uncertainties are discussed for two Australian vegetation condition indices, BioMetric and Habitat Hectares. It is concluded that the nature of uncertainties in estimates of current and future vegetation condition may increase the risk that any given decision will fail to achieve No Net Loss of biodiversity. Chapters 3 to 5 evaluate sources of uncertainty in current estimates of vegetation condition. Chapter 3 uses empirical biodiversity data to evaluate whether, on average, sites with higher vegetation condition scores support a greater diversity of native species than sites with lower scores. The strength of relationships between species composition and condition scores was primarily driven by plant species, which is included as a predictor variable in both BioMetric and Habitat Hectares. Vegetation condition was very poorly correlated with the richness and diversity of native butterflies and native ants, with the possible exception of very low scoring sites for butterflies. The results suggest that patterns in species composition were driven by factors other than the predictor variables included in the indices, and therefore that conceptual uncertainty may be a substantial cause of poor performance of vegetation condition indices. Chapter 4 empirically investigates the magnitude of uncertainty in estimates of current vegetation condition due to observer error in field estimates of predictor variables. Average coefficients of variation in total vegetation condition scores amongst ten independent observers were 15-18%. All observers estimated vegetation condition scores that were substantially different from the group mean on at least some sites. The results indicate that measurement error in field estimates of site attributes may cause vegetation condition to be under- or over-estimated on all but highly degraded sites. Chapter 5 examines the sensitivity of vegetation condition indices to observer error via simulated scenarios. Larger observer errors caused less precision and greater bias in total scores, although compensatory errors generally led to smaller coefficients of variation in total scores than predictor variables. Unexpectedly, unbiased observer errors in the predictor variables underestimated the true vegetation condition of most sites. The underestimation effect was more significant for sites with intact woody or herbaceous features, depending on the index used. Chapters 4 and 5 highlight the fact that quantitative aspects of vegetation condition indices are as important as the spread and bias of raw observer estimates in determining accuracy of vegetation condition assessments. These operational limitations of vegetation condition indices may significantly increase the risk of worse than expected biodiversity outcomes. Chapter 6 examines the implications of uncertainty in estimates of predicted future vegetation condition for achieving No Net Loss in biodiversity offsets. Expert models of change in 12 vegetation attributes were used to simulate change over time for five states of a grassy woodland ecosystem under six (gain and loss) management scenarios. The quantity of gains that would be required to compensate for each loss scenario (i.e. the offset ratio) was calculated using one method that ignored uncertainty and another that accounted for it. Uncertainty increased the offset ratio up to 1400% where the magnitude of both gains and losses were uncertain, but increased the ratio only marginally where minimal losses were incurred on highly degraded site types and offset with maximal gains. Both vegetation condition indices predicted greatest gains in woody vegetation attributes, which may result in landscape wide decline in herbaceous components of vegetation and their associated biodiversity if policies aim to maximise gains in vegetation condition. The results of this research indicate that aspects of the conceptual, quantitative and data models that underpin biodiversity valuation indices are likely to cause estimates of current and future biodiversity value to be unreliable. Outcomes of market based biodiversity conservation policies would greatly benefit from more rigorous procedures for developing and evaluating biodiversity valuation indices, which systematically identify and minimise uncertainties in the underpinning models. Information about uncertainty should be used in a risk-based approach to decision making in market based policies, whereby only low risk decisions are approved. It will be a shame if the pioneering work Australia has conducted in developing market based instruments for biodiversity conservation, and associated vegetation condition indices, is not used to fully evaluate the potential for overcoming market externalities and achieving optimal biodiversity outcomes for society.
  • Item
    Thumbnail Image
    The function and evolution of the dinoflagellate mitochondrion
    Ackland, Jillian Clare (University of Melbourne, 2010)
    The mitochondrion is a highly evolved, indispensable organelle found in all eukaryotes. This compartment has undergone metabolic and functional changes as cell lineages have diversified and specialised throughout evolution. Alveolata is a well-defined group of single-celled eukaryotes that encompasses related Phyla with extremely diverse lifestyles. Most alveolates belong to one of three main subgroups: predatory ciliates, endoparasitic apicomplexans, and heterotrophic or autotrophic dinoflagellates. Little is known about the biology of the dinoflagellate mitochondrion and studying this compartment offers an opportunity to examine organelle evolution within the alveolate lineage. In this study, I have used the dinoflagellate Karlodinium micrum, as a model to examine mitochondrial evolution. I have investigated the evolution of (1) genes, (2) biochemical functions and (3) protein targeting mechanisms of this organelle. Organelles can replace and gain genes by endosymbiotic gene transfer (EGT, genes derived from an endosymbiont) and lateral gene transfer (LOT, genes derived from an external source). Dinoflagellates have shown a unique propensity to replace their plastids with plastids of other algae during evolution and K. micrum represents a dinoflagellate lineage that has replaced its ancestral plastid with an endosymbiont derived from a haptophyte. In this case, haptophyte endosymbiont plastid genes are located in the dinoflagellate nucleus, providing evidence of EGT in this system. I have assessed if the mitochondrial proteome of K. micrum has been remodelled by EGT and/or LTG. Genes encoding mitochondrial proteins have been identified from a K. micrum expressed sequence tag library and their evolutionary origins inferred by phylogenetics. Several mitochondrial genes are derived from an external source but none originate from the haptophyte endosymbiont, indicating that the K. micrum mitochondrial proteome has been minimally impacted by this endosymbiotic event, but is nevertheless genetically dynamic. Plasmodium falciparum, the disease agent that causes malaria, is a member of Apicomplexa. This protist has a mitochondrion that has been described as metabolically reduced compared to canonical mitochondria, change that has been attributed to the parasitic lifestyle this organism leads. In this thesis, I test whether or not perceived reduction in apicomplexan mitochondrial metabolism is a result of parasitism. A putative metabolic map of the dinoflagellate mitochondrion has been constructed and compared to what is currently known about the mitochondrial biochemistry of closely related apicomplexan parasites and a free living basal alveolate, the ciliate Tetrahymena thermophila. This is the first report of a broad analysis of the mitochondrial metabolism of a dinoflagellate. The mitochondrion of K. micrum shows broad metabolic conservation, having retained pathways implicated in ATP generation by oxidative phosphorylation. Several changes in the metabolism of the P. falciparum mitochondrion were also observed in K. micrum and/or T. thermophila, suggesting that these modifications are not due to parasitism. The presence of most components of the tricarboxylic acid cycle, in addition to what is most likely a functional electron transport chain and ATP synthase complex in both dinoflagellates and P. falciparum indicates that the mitochondrion of the Plasmodium parasite is probably implicated in ATP generation by oxidative phosphorylation. The diversification of dinoflagellates has been accompanied by considerable changes in plastid protein targeting signals, but it is unclear whether or not mitochondrial protein targeting in this lineage has also been modified. In the final experimental chapter of this thesis I have assessed the conservation of mitochondrial protein import mechanisms in dinoflagellates. Genes for K. micrum mitochondrial proteins have been analysed for mitochondrial protein targeting signals using bioinformatic tools, and the function of these signals has been tested using the reporter molecule green fluorescent protein (GFP) and a heterologous yeast expression system. Amino-terminal and internal mitochondrial targeting signals of K. micrum mitochondrial precursors are sufficiently conserved for recognition and import into yeast mitochondria, indicating that dinoflagellate mitochondrial protein targeting signals have been highly conserved, since early in eukaryotic diversification. Overall, my investigations of the dinoflagellate mitochondrion, and this broad comparative analysis of alveolate mitochondria has shown that aspects of mitochondrial biology (ie. mitochondrial gene compliment, mitochondrial biochemistry and function, and mitochondrial protein targeting) have evolved differently during the diversification of alveolates. Alveolate mitochondria are genetically flexible, having experienced gene gains and gene losses. This variation is not always accompanied by functional divergence, and does not necessarily reflect the lifestyle/nutritional requirements of the host. Thus while the mitochondrion is clearly an innovative compartment, its evolutionary behaviour cannot be characterised based on any one aspect of its cell biology alone.
  • Item
    Thumbnail Image
    Fungal diversity in remnant vegetation patches along an urban to rural gradient
    Newbound, Mark Gavin. (University of Melbourne, 2008)
    Remnant vegetation patches in urban areas are valuable for biodiversity conservation, as well as recreation and community education. Fungi are a functionally important, and often overlooked, aspect of the diversity of remnants. Fungi are highly diverse, accounting for around 8% of the world�s species. They are critical in food webs and for nutrient cycling. Symbiotic mycorrhizal relationships between plants and fungi are important for plant nutrition, seedling establishment, and can affect the composition of plant communities. This thesis presents an investigation into how the distribution and occurrence of fungi in remnants are influenced by the level of surrounding urbanisation. The research was set in the city of Melbourne, Victoria. Surveys were made of both above and below ground fungal structures in remnant vegetation patches along an urban to rural gradient. Above ground, species of macrofungi were surveyed over two years by the collection and identification of fruiting bodies. Two below ground surveys were made. In the first, mycorrhizal root tips of two eucalypt species were sampled along a gradient. The second used a molecular method, terminal restriction length polymorphism (TRFLP), to assess diversity in bulk soil samples taken from sites. The fruiting body surveys produced the most informative results. Distinctions were made between properties affecting saprotrophic species, which derive carbohydrates from decaying organic matter, and ectomycorrhizal (ECM) fungi, which obtain carbohydrates from symbiotic plant hosts. A total of 199 species were found, with close to four times more saprotrophic than ECM species. Urbanisation appeared to have little effect on diversity, which was influenced more by particular site properties. Saprotrophic species richness decreased with increasing canopy openness; ECM richness decreased with higher soil pH and available phosphorus; and the ratio of saprotrophs to ECM increased with greater soil nitrate. Some management practices based on the findings are suggested to promote fungal diversity within urban remnants. A second topic in the thesis is an investigation of methods used to survey fungi. Assessments of fungal diversity are problematic because fungi are cryptic, highly diverse and patchily distributed. To help improve the efficiency of fruiting body surveys, Bayesian models were made to identify the environmental factors that influence fruiting. These suggested that to increase the probability of detecting species, frequent fruiting body surveys should be made in late autumn to early winter when the average value for rainfall minus evaporation for the previous 28 days is above -1 mm per day. Analyses were also made to compare the efficiency of the fruiting body and TRFLP survey methods. These found that species present were four times more likely to be found using TRFLP. However the TRFLP results did not correlate with environmental properties, probably because different fungal functional groups could not be differentiated. Thus, although less efficient for finding the total number of species present, fruiting body surveys provided a more representative sample of the fungal community. In conclusion, remnant vegetation in urban settings appears to be a valuable repository of macrofungal diversity, although doubts remain because of the limits of the surveying methods used.
  • Item
    Thumbnail Image
    Microprobe-localisation and ecophysiological studies of manganese-hyperaccumulating plants
    Fernando, Denise Rita Marie. (University of Melbourne, 2008)
  • Item
    Thumbnail Image
    The regulation of sirodesmin PL biosynthesis in the plant pathogenic fungus, leptosphaeria maculans
    Fox, Ellen M. (University of Melbourne, 2008)
    Sirodesmin PL is an epipolythiodioxopiperazine (ETP) toxin produced by the ascomycete Leptosphaeria maculans, which causes blackleg disease of canola (Brassica napus). This toxin is required for full virulence of L. maculans on stems of B. napus. Previous studies have shown that sirodesmin PL biosynthesis involves a cluster of 18 co-regulated genes and that disruption of the non-ribosomal peptide synthetase gene (sirP) in this cluster prevents the production of sirodesmin PL. The aim of my project was to determine how the production of sirodesmin PL is regulated. Two approaches were used to determine this. The first approach involved RNAi-mediated silencing of a candidate regulator, sirZ, encoded within the sirodesmin PL biosynthetic gene cluster. This gene encodes a putative Zn(II)2Cys6 DNA-binding protein, SirZ. The RNAi-mediated silencing of sirZ transcription revealed that SirZ is responsible for the regulation of sirodesmin PL production, via regulating the transcription of cluster genes. The second approach was to screen a library of L. maculans T-DNA insertional mutants for sirodesmin-deficient isolates and then determine the identity of the mutated gene(s). Four sirodesmin-deficient isolates were identified in a screen of over 200 L. maculans insertional mutants. Further characterization of these four mutants revealed that each contained a single T-DNA insertion in non-coding regions of the genome. The genes closest to each of the T-DNA insertion sites were a putative secreted protein, a conserved hypothetical protein, a putative transcription factor and a gene showing sequence similarity to fungal regulators of the cross-pathway control system. The role of the latter gene (named LmcpcA) in the regulation of sirodesmin PL production was analysed further using RNAi-mediated silencing. Under nutrient-rich conditions, the RNAi-mediated silencing of LmcpcA did not affect the regulation of sirodesmin PL production or transcription of sirodesmin PL biosynthetic genes, sirZ and sirP. However, upon amino acid starvation, silencing of LmcpcA transcription resulted in enhanced transcription of sirZ and sirP, compared to the wild type strain. These findings suggest that LmcpcA plays a role in the regulation of sirodesmin PL production in L. maculans in response to amino acid availability. Another ascomycete, Aspergillus fumigatus produces the well-characterized ETP, gliotoxin. To determine if the regulation of ETP production is conserved across fungi, an A. fumigatus mutant carrying a deletion in the pathway-specific regulator of gliotoxin production, gliZ (created by Dr. Jin-Woo Bok from Prof. Nancy Keller�s laboratory), was transformed with an entire copy of L. maculans sirZ or PlgliZ, the putative pathway-specific regulator of gliotoxin production in Pencillium lilacinoechinulatum. Complementation was not observed. Bioinformatic analysis of upstream regions of ETP biosynthetic genes in A. fumigatus, L. maculans and P. lilacinoechinulatum led to the prediction of a conserved binding element for GliZ, SirZ and PIGliZ, respectively. The step in the biosynthetic pathway whereby sulphur molecules are introduced into the core ETP structure has not been described, but has been proposed to involve cysteine as the sulphur donor. This step is thought to be catalysed by gene products of ETP cluster genes gliI or sirI, in A. fumigatus and L. maculans, respectively. Analysis of an A. fumigatus mutant carrying a deletion of gliI revealed that this gene is essential for gliotoxin production. The potential role of this gene in gliotoxin (or sirodesmin PL) production remains unknown.
  • Item
    Thumbnail Image
    Dissecting antibiotic targeting in the malaria parasite Plasmodium falciparum
    Johnson, Russell Andrew. (University of Melbourne, 2008)
  • Item
    Thumbnail Image
    Phylogeny and biogeography of eucalyptus subgenus Eudesmia
    Gibbs, Adele Katherine. (University of Melbourne, 2007)
    Eucalyptus L�H�r. (Myrtaceae) is a dominant feature of the Australian landscape and an ecologically and economically important genus for the timber industry, for the distillation of essential oils and as native vegetation. Within Eucalyptus, three main clades are recognized as subgenera: Eudesmia, Symphyomyrtus and Eucalyptus. Subgenus Eudesmia currently includes 26 species and subspecies that are distributed across the tropical � temperate regions of Western Australia, Northern Territory, Queensland and the central arid deserts of Western Australia and South Australia, and the focus of this thesis. The classification and phylogeny of subg. Eudesmia to date are poorly resolved, and require further investigation. The aims of this project were to determine the phylogenetic relationships of the eudesmid eucalypts using molecular and morphological data, and to investigate the historical biogeography of the eudesmid group. The phylogeny is used as the basis of a revised classification and to identify key diagnostic morphological characters. A phylogeny including all taxa in subg. Eudesmia was constructed using DNA sequences of the internal transcribed spacer (ITS) and the external transcribed spacer (ETS) regions from nuclear ribosomal DNA, the psbA-trnH intergenic spacer region from chloroplast DNA, and morphology, including a glasshouse trial to raise seedlings from seed. Parsimony analyses were conducted using PAUP* and Bayesian inference using MrBayes computer programs. Pseudogenes were identified for the ITS-1 region, and thus the ITS-1 region was excluded from this study. Three indels were scored as informative from the molecular regions. Morphological characters were defined from adult leaves, buds, flowers, fruit, seedling leaf shape and arrangement. Scanning electron microscopy and light microscopy were used to study the seeds, trichomes, and floral characters. The characters were coded as binary or multistate, with quantitative characters gap-coded. Thirty two informative characters were identified, and included fruit shape, seed shape, cotyledon size and shape, trichome type, ovule row number and the leaf stage of trichome loss. Paralogy-free subtree analysis was used to understand the historical relationships of the biogeographic areas where eudesmids occur. The minimum area tree (with 100% consistency) had a basal trichotomy of: MacPherson/Macleay area, a clade of �Western� areas, including the Northern Desert, Pilbara, Western Desert, Geraldton Sandplains and Interzone, and northern and eastern areas, from the Kimberley to Cape York and Queensland. The eudesmids appear to reflect two biogeographic tracks found in previous studies, (1) Northern-Eastern Australia, and (2) South West WA and desert areas. Vicariance barriers can be correlated with ecological and historical events, and have various ages ranging from the Eocene to the Pleistocene. A summary tree with the greatest resolution was constructed from the congruent clades from all the molecular and morphological phylogenies. Five taxonomic series are recommended in a revised classification. The largest series is Eudesmieae, which includes fourteen species, and is further divided into five subseries and two superspecies. Most of these species have stamens in four bundles, and this series is congruent with Pryor and Johnson�s series Tetragonae. The other series are Similes (E. lirata and E. similis), Baileyanae (E. baileyana), Tetrodontae (E. tetrodonta), and Miniatae with five species.