School of Botany - Research Publications
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ItemComparison of transcription of multiple genes at three developmental stages of the plant pathogen Sclerotinia sclerotiorum(BLACKWELL PUBLISHING, 2006-05)The ascomycete Sclerotinia sclerotiorum is a plant pathogen with a very broad host range. In order to identify and characterize genes involved in S. sclerotiorum infection of Brassica napus (canola), expressed sequence tags (ESTs) were examined from libraries prepared from three tissues: complex appressorium (infection cushions), mycelia grown on agar and lesions formed on leaves of B. napus. A high proportion of genes (68%) had not been previously reported for S. sclerotiorum in public gene or EST databases. The types of novel genes identified in the infection cushion library highlights the functional specificity of these structures and similarities to appressoria in other fungal pathogens. Quantitative real-time PCR was used to analyse tissue specificity and timing of transcription of genes with best matches to MAS3 (appressoria-associated protein from Magnaporthe grisea), cellobiohydrolase I, oxaloacetate acetylhydrolase, metallothionein, pisatin demethylase, and an unknown gene with orthologs in fungal pathogens but not in saprophytic fungi.
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ItemPopulation structure of Sclerotinia sclerotiorum in an Australian canola field at flowering and stem-infection stages of the disease cycle(NATL RESEARCH COUNCIL CANADA-N R C RESEARCH PRESS, 2006-11)Populations of the ascomycete pathogen Sclerotinia sclerotiorum sampled from a canola field were analysed using microsatellite markers. Fifty isolates were collected from ascospore-infested canola petals and, later in the season, another 55 isolates were obtained from stem lesions; these isolates were used to compare inoculum and disease-causing populations. Fifty-five unique haplotypes were identified, with gene diversity ranging from 0.40 to 0.71. Genotypic diversity was higher in the inoculum population than it had been in the previous year, but analysis of molecular variance (AMOVA) showed that less than 10% of the variation was attributable to differences between the 2 years. Genotypic disequilibrium measures were consistent with the occurrence of both clonal reproduction and out-crossing. There was no significant population subdivision between the ascospore and stem-lesion populations, as measured with fixation indices (R(ST) = 0.015, p = 0.90) and AMOVA, suggesting that there are no genetically defined subgroups of isolates more likely to proceed from petal colonization to cause stem infection. This might be because S. sclerotiorum possesses wide-ranging pathogenicity mechanisms that account for the lack of host specificity observed to date.
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ItemParallels in fungal pathogenesis on plant and animal hosts(AMER SOC MICROBIOLOGY, 2006-12)
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ItemMembrane transporters in the relict plastid of malaria parasites(NATL ACAD SCIENCES, 2006-06-20)Malaria parasites contain a nonphotosynthetic plastid homologous to chloroplasts of plants. The parasite plastid synthesizes fatty acids, heme, iron sulfur clusters and isoprenoid precursors and is indispensable, making it an attractive target for antiparasite drugs. How parasite plastid biosynthetic pathways are fuelled in the absence of photosynthetic capture of energy and carbon was not clear. Here, we describe a pair of parasite transporter proteins, PfiTPT and PfoTPT, that are homologues of plant chloroplast innermost membrane transporters responsible for moving phosphorylated C3, C5, and C6 compounds across the plant chloroplast envelope. PfiTPT is shown to be localized in the innermost membrane of the parasite plastid courtesy of a cleavable N-terminal targeting sequence. PfoTPT lacks such a targeting sequence, but is shown to localize in the outermost parasite plastid membrane with its termini projecting into the cytosol. We have identified these membrane proteins in the parasite plastid and determined membrane orientation for PfoTPT. PfiTPT and PfoTPT are proposed to act in tandem to transport phosphorylated C3 compounds from the parasite cytosol into the plastid. Thus, the transporters could shunt glycolytic derivatives of glucose scavenged from the host into the plastid providing carbon, reducing equivalents and ATP to power the organelle.
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ItemComplete nucleotide sequence of the chlorarachniophyte nucleomorph: Nature's smallest nucleus(NATL ACAD SCIENCES, 2006-06-20)The introduction of plastids into different heterotrophic protists created lineages of algae that diversified explosively, proliferated in marine and freshwater environments, and radically altered the biosphere. The origins of these secondary plastids are usually inferred from the presence of additional plastid membranes. However, two examples provide unique snapshots of secondary-endosymbiosis-in-action, because they retain a vestige of the endosymbiont nucleus known as the nucleomorph. These are chlorarachniophytes and cryptomonads, which acquired their plastids from a green and red alga respectively. To allow comparisons between them, we have sequenced the nucleomorph genome from the chlorarachniophyte Bigelowiella natans: at a mere 373,000 bp and with only 331 genes, the smallest nuclear genome known and a model for extreme reduction. The genome is eukaryotic in nature, with three linear chromosomes containing densely packed genes with numerous overlaps. The genome is replete with 852 introns, but these are the smallest introns known, being only 18, 19, 20, or 21 nt in length. These pygmy introns are shown to be miniaturized versions of normal-sized introns present in the endosymbiont at the time of capture. Seventeen nucleomorph genes encode proteins that function in the plastid. The other nucleomorph genes are housekeeping entities, presumably underpinning maintenance and expression of these plastid proteins. Chlorarachniophyte plastids are thus serviced by three different genomes (plastid, nucleomorph, and host nucleus) requiring remarkable coordination and targeting. Although originating by two independent endosymbioses, chlorarachniophyte and cryptomonad nucleomorph genomes have converged upon remarkably similar architectures but differ in many molecular details that reflect two distinct trajectories to hypercompaction and reduction.
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ItemHabitat utilisation by small mammals in a coastal heathland exhibiting symptoms of Phytophthora cinnamomi infestation(CSIRO Publishing, 2006-12-01)Phytophthora cinnamomi is a soil-inhabiting ‘water mould’ that is pathogenic to many native plant species in Australia, and has been shown to alter plant species abundance and richness, as well as the structure of vegetation in sclerophyllous vegetation. This study investigated the effects of P. cinnamomi-induced vegetation disturbance and habitat degradation on microhabitat associations of small mammals in a coastal heathland in southern Australia. Seven small mammal species were trapped in a P. cinnamomi-infested heathland community over four years. Trap stations were classified into three disease classes (non-diseased, active disease and post-disease) and structural and floristic aspects of the vegetation were recorded at each station. The mean number of species captured was greatest in non-diseased areas and least in post-disease areas. The total capture frequency of small mammals was lower in post-disease areas except where they were covered by thick stands of tall tea-tree (Leptospermum sp.). Combined small mammal captures were associated with thick vegetation and floristic factors. Captures of Antechinus agilis, Rattus fuscipes, Rattus lutreolus and Sminthopsis leucopus were greatest in non-diseased vegetation and were less frequent in areas of diseased vegetation. A. agilis and R. fuscipes captures were correlated with a floristic factor associated with non-diseased vegetation, while R. lutreolus was associated with structural factors, preferring thick vegetation. The impact on Cercartetus nanus and Isoodon obesulus could not be assessed owing to low captures of these species. Modification of vegetation structure and floristics associated with P. cinnamomi infestation is having a significant impact on the habitat utilised by the small mammal communities in the area. This impact highlights the need to identify and protect those areas that remain free of P. cinnamomi infestation. Continued spread of the pathogen will reduce the area of suitable small-mammal habitat able to support the diverse communities of the eastern Otway Ranges, Victoria, Australia.
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ItemGrowth cost and ontogenetic expression patterns of defence in cyanogenic Eucalyptus spp.(SPRINGER HEIDELBERG, 2006-11)
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ItemVariation in protein abundance profiles in the M-semitendinosus of lambs bred from sires selected on the basis of growth and muscling potential(CSIRO PUBLISHING, 2006)Relative abundance of proteins localised in the nuclear-enriched, total cell membrane and cytosolic fractions of the semitendinosus muscle was compared between lambs bred from control (C), high muscling (M), and high growth rate (G) sires. In total, 31 proteins were identified whose abundance was differentially regulated between sire type. Differences in hind-limb muscle development between M lambs and C and G lambs were reflected in levels of proteins that regulate or function in cellular mechanisms of protein and energy metabolism. Despite no apparent difference in hind-limb muscle growth in G lambs compared to C, G lambs exhibited marked differences in proteins involved in regulation and function of energy metabolism. These results detail pathways that can be specifically targeted to enhance muscle accretion and growth in lambs. The development of means to manipulate these cellular mechanisms may yield greater gains in muscle accretion and growth rate than breeding on the basis for genetic capacity alone.