School of BioSciences - Research Publications
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ItemEpidermal bladder cells confer salinity stress tolerance in the halophyte quinoa and Atriplex species(WILEY, 2017-09-01)Epidermal bladder cells (EBCs) have been postulated to assist halophytes in coping with saline environments. However, little direct supporting evidence is available. Here, Chenopodium quinoa plants were grown under saline conditions for 5 weeks. One day prior to salinity treatment, EBCs from all leaves and petioles were gently removed by using a soft cosmetic brush and physiological, ionic and metabolic changes in brushed and non-brushed leaves were compared. Gentle removal of EBC neither initiated wound metabolism nor affected the physiology and biochemistry of control-grown plants but did have a pronounced effect on salt-grown plants, resulting in a salt-sensitive phenotype. Of 91 detected metabolites, more than half were significantly affected by salinity. Removal of EBC dramatically modified these metabolic changes, with the biggest differences reported for gamma-aminobutyric acid (GABA), proline, sucrose and inositol, affecting ion transport across cellular membranes (as shown in electrophysiological experiments). This work provides the first direct evidence for a role of EBC in salt tolerance in halophytes and attributes this to (1) a key role of EBC as a salt dump for external sequestration of sodium; (2) improved K+ retention in leaf mesophyll and (3) EBC as a storage space for several metabolites known to modulate plant ionic relations.
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ItemMapping carbon fate during bleaching in a model cnidarian symbiosis: the application of C-13 metabolomics(WILEY, 2017-06-01)Coral bleaching is a major threat to the persistence of coral reefs. Yet we lack detailed knowledge of the metabolic interactions that determine symbiosis function and bleaching-induced change. We mapped autotrophic carbon fate within the free metabolite pools of both partners of a model cnidarian-dinoflagellate symbiosis (Aiptasia-Symbiodinium) during exposure to thermal stress via the stable isotope tracer (13 C bicarbonate), coupled to GC-MS. Symbiont photodamage and pronounced bleaching coincided with substantial increases in the turnover of non13 C-labelled pools in the dinoflagellate (lipid and starch store catabolism). However, 13 C enrichment of multiple compounds associated with ongoing carbon fixation and de novo biosynthesis pathways was maintained (glucose, fatty acid and lipogenesis intermediates). Minimal change was also observed in host pools of 13 C-enriched glucose (a major symbiont-derived mobile product). However, host pathways downstream showed altered carbon fate and/or pool composition, with accumulation of compatible solutes and nonenzymic antioxidant precursors. In hospite symbionts continue to provide mobile products to the host, but at a significant cost to themselves, necessitating the mobilization of energy stores. These data highlight the need to further elucidate the role of metabolic interactions between symbiotic partners, during the process of thermal acclimation and coral bleaching.
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ItemLipidomics reveal the protective effects of a vegetable-derived isothiocyanate against retinal degeneration.(F1000 Research Ltd, 2019)Background: Age-related macular degeneration (AMD) is a leading cause of blindness in the ageing population. Without effective treatment strategies that can prevent disease progression, there is an urgent need for novel therapeutic interventions to reduce the burden of vision loss and improve patients' quality of life. Dysfunctional innate immune responses to oxidative stress observed in AMD can be caused by the formation of oxidised lipids, whilst polyunsaturated fatty acids have shown to increase the risk of AMD and disease progression in affected individuals. Previously, our laboratory has shown that the vegetable-derived isothiocyanate, L-sulforaphane (LSF), can protect human adult pigment epithelial cells from oxidative damage by upregulating gene expression of the oxidative stress enzyme Glutathione-S-Transferase µ1. This study aims to validate the protective effects of LSF on human retinal cells under oxidative stress conditions and to reveal the key players in fatty acid and lipid metabolism that may facilitate this protection. Methods: The in vitro oxidative stress model of AMD was based on the exposure of an adult retinal pigment epithelium-19 cell line to 200µM hydrogen peroxide. Percentage cell proliferation following LSF treatment was measured using tetrazolium salt-based assays. Untargeted fatty acid profiling was performed by gas chromatography-mass spectrometry. Untargeted lipid profiling was performed by liquid chromatography-mass spectrometry. Results: Under hydrogen peroxide-induced oxidative stress conditions, LSF treatment induced dose-dependent cell proliferation. The key fatty acids that were increased by LSF treatment of the retinal cells include oleic acid and eicosatrienoic acid. LSF treatment also increased levels of the lipid classes phosphatidylcholine, cholesteryl ester and oxo-phytodienoic acid but decreased levels of phosphatidylethanolamine lipids. Conclusions: We propose that retinal cells at risk of oxidative damage and apoptosis can be pre-conditioned with LSF to regulate levels of selected fatty acids and lipids known to be implicated in the pathogenesis and progression of AMD.
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ItemComparative metabolomics implicates threitol as a fungal signal supporting colonization of Armillaria luteobubalina on eucalypt roots(WILEY, 2019-12-03)Armillaria root rot is a fungal disease that affects a wide range of trees and crops around the world. Despite being a widespread disease, little is known about the plant molecular responses towards the pathogenic fungi at the early phase of their interaction. With recent research highlighting the vital roles of metabolites in plant root-microbe interactions, we sought to explore the presymbiotic metabolite responses of Eucalyptus grandis seedlings towards Armillaria luteobuablina, a necrotrophic pathogen native to Australia. Using a metabolite profiling approach, we have identified threitol as one of the key metabolite responses in E. grandis root tips specific to A. luteobubalina that were not induced by three other species of soil-borne microbes of different lifestyle strategies (a mutualist, a commensalist, and a hemi-biotrophic pathogen). Using isotope labelling, threitol detected in the Armillaria-treated root tips was found to be largely derived from the fungal pathogen. Exogenous application of d-threitol promoted microbial colonization of E. grandis and triggered hormonal responses in root cells. Together, our results support a role of threitol as an important metabolite signal during eucalypt-Armillaria interaction prior to infection thus advancing our mechanistic understanding on the earliest stage of Armillaria disease development. Comparative metabolomics of eucalypt roots interacting with a range of fungal lifestyles identified threitol enrichment as a specific characteristic of Armillaria pathogenesis. Our findings suggest that threitol acts as one of the earliest fungal signals promoting Armillaria colonization of roots.
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ItemRelaxin reduces endothelium-derived vasoconstriction in hypertension: Revealing new therapeutic insights(WILEY, 2019-10-31)BACKGROUND AND PURPOSE: Endothelium-derived vasoconstriction is a hallmark of vascular dysfunction in hypertension. In some cases, an overproduction of endothelium-derived prostacyclin (PGI2 ) can cause contraction rather than relaxation. Relaxin is well known for its vasoprotective actions, but the possibility that this peptide could also reverse endothelium-derived vasoconstriction has never been investigated. We tested the hypothesis that short-term relaxin treatment mitigates endothelium-derived vasoconstriction in spontaneously hypertensive rats (SHR). EXPERIMENTAL APPROACH: Male Wistar Kyoto rats (WKY) and SHR were subcutaneously infused with either vehicle (20 mmol·L-1 sodium acetate) or relaxin (13.3 μg·kg-1 ·hr-1 ) using osmotic minipumps for 3 days. Vascular reactivity to the endothelium-dependent agonist ACh was assessed in vitro by wire myography. Quantitative PCR and LC-MS were used to identify changes in gene expression of prostanoid pathways and PG production, respectively. KEY RESULTS: Relaxin treatment ameliorated hypertension-induced endothelial dysfunction by increasing NO-dependent relaxation and reducing endothelium-dependent contraction. Notably, short-term relaxin treatment up-regulated mesenteric PGI2 receptor (IP) expression, permitting PGI2 -IP-mediated vasorelaxation. In the aorta, reversal of contraction was accompanied by suppression of the hypertension-induced increase in prostanoid-producing enzymes and reduction in PGI2 -evoked contractions. CONCLUSIONS AND IMPLICATIONS: Relaxin has region-dependent vasoprotective actions in hypertension. Specifically, relaxin has distinct effects on endothelium-derived contracting factors and their associated vasoconstrictor pathways in mesenteric arteries and the aorta. Taken together, these observations reveal the potential of relaxin as a new therapeutic agent for vascular disorders that are associated with endothelium-derived vasoconstriction including hypertension.
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ItemAndrogen receptor antagonism accelerates disease onset in the SOD1(G93A) mouse model of amyotrophic lateral sclerosis(WILEY, 2019-07-01)BACKGROUND AND PURPOSE: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease typically more common in males, implicating androgens in progression of both patients and mouse models. Androgen effects are mediated by androgen receptor which is highly expressed in spinal motor neurons and skeletal muscles. To clarify the role of androgen receptors in ALS, we therefore examined the effect of androgen receptor antagonism in the SOD1G93A mouse model. EXPERIMENTAL APPROACH: The androgen receptor antagonist, flutamide, was administered to presymptomatic SOD1G93A mice as a slow-release subcutaneous implant (5 mg·day-1 ). Testosterone, flutamide, and metabolite levels were measured in blood and spinal cord tissue by LC-MS-MS. Effects on disease onset and progression were assessed using motor function tests, survival, muscle, and neuropathological analyses. KEY RESULTS: Flutamide was metabolised to 2-hydroxyflutamide achieving steady-state plasma levels across the study duration and reached the spinal cord at pharmacologically active concentrations. Flutamide treatment accelerated disease onset and locomotor dysfunction in male SOD1G93A mice, but not female mice, without affecting survival. Analysis of hindlimb muscles revealed exacerbation of myofibre atrophy in male SOD1G93A mice treated with flutamide, although motor neuron pathology was not affected. CONCLUSION AND IMPLICATIONS: The androgen receptor antagonist accelerated disease onset in male SOD1G93A mice, leading to exacerbated muscle pathology, consistent with a role of androgens in modulating disease severity, sexual dimorphism, and peripheral pathology in ALS. These results also demonstrate a key contribution of skeletal muscle pathology to disease onset, but not outcome, in this mouse model of ALS.
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ItemSingle cell-type analysis of cellular lipid remodelling in response to salinity in the epidermal bladder cells of the model halophyte Mesembryanthemum crystallinum(WILEY, 2018-10-01)Salt stress causes dramatic changes in the organization and dynamic properties of membranes, however, little is known about the underlying mechanisms involved. Modified trichomes, known as epidermal bladder cells (EBC), on the leaves and stems of the halophyte Mesembryanthemum crystallinum can be successfully exploited as a single-cell-type system to investigate salt-induced changes to cellular lipid composition. In this study, alterations in key molecular species from different lipid classes highlighted an increase in phospholipid species, particularly those from phosphatidylcholine and phosphatidic acid (PA), where the latter is central to the synthesis of membrane lipids. Triacylglycerol (TG) species decreased during salinity, while there was little change in plastidic galactolipids. EBC transcriptomic and proteomic data mining revealed changes in genes and proteins involved in lipid metabolism and the upregulation of transcripts for PIPKIB, PI5PII, PIPKIII, and phospholipase D delta suggested the induction of signalling processes mediated by phosphoinositides and PA. TEM and flow cytometry showed the dynamic nature of lipid droplets in these cells under salt stress. Altogether, this work indicates that the metabolism of TG might play an important role in EBC response to salinity as either an energy reserve for sodium accumulation and/or driving membrane biosynthesis for EBC expansion.
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ItemWater availability moderates N-2 fixation benefit from elevated [CO2]: A 2-year free-air CO2 enrichment study on lentil (Lens culinaris MEDIK.) in a water limited agroecosystem(WILEY, 2018-10-01)Increased biomass and yield of plants grown under elevated [CO2 ] often corresponds to decreased grain N concentration ([N]), diminishing nutritional quality of crops. Legumes through their symbiotic N2 fixation may be better able to maintain biomass [N] and grain [N] under elevated [CO2 ], provided N2 fixation is stimulated by elevated [CO2 ] in line with growth and yield. In Mediterranean-type agroecosystems, N2 fixation may be impaired by drought, and it is unclear whether elevated [CO2 ] stimulation of N2 fixation can overcome this impact in dry years. To address this question, we grew lentil under two [CO2 ] (ambient ~400 ppm and elevated ~550 ppm) levels in a free-air CO2 enrichment facility over two growing seasons sharply contrasting in rainfall. Elevated [CO2 ] stimulated N2 fixation through greater nodule number (+27%), mass (+18%), and specific fixation activity (+17%), and this stimulation was greater in the high than in the low rainfall/dry season. Elevated [CO2 ] depressed grain [N] (-4%) in the dry season. In contrast, grain [N] increased (+3%) in the high rainfall season under elevated [CO2 ], as a consequence of greater post-flowering N2 fixation. Our results suggest that the benefit for N2 fixation from elevated [CO2 ] is high as long as there is enough soil water to continue N2 fixation during grain filling.
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Item2015: an eventful year for the Metabolomics Society(SPRINGER, 2015-12-01)
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ItemOne minute with the Metabolomics Society's Honorary Fellows 2015(SPRINGER, 2015-08-01)