Biology subjects

McDonald, M.

Publications and source records attributed to McDonald, M..

3 recordsLinked to original sources

bioRxiv2018

Acquisition and loss of secondary metabolite clusters shaped the evolutionary path of three recently emerged phytopathogens of wheat

O_LIWhite grain disorder is a recently emerged wheat disease in Australia, caused by three Botryosphaeriaceae spp.; Eutiarosporella darliae, E. pseudodarliae, and E. tritici-australis. The disease cycle of these pathogens and the molecular basis of their interaction with wheat are poorly understood. To address this, we undertook a comparative genomics approach to identify potential pathogenicity factors.\nC_LIO_LISubsequent genome analysis revealed that each of the white grain disorder species harbour modular polyketide synthase genes. To our knowledge, this is the first report of fungi harbouring such genes. Further comparative analysis using the modular polyketide synthase genes discovered their presence in the closely related Macrophomina phaseolina. Phylogenetic analysis implicates horizontal acquisition of these genes from a bacterial or a protist species.\nC_LIO_LIBoth E. darliae and E. pseudodarliae possess a secondary metabolite cluster with multiple polyketide/non-ribosomal peptide synthase genes (Hybrid-1, -2, and -3). In contrast, only remnant and partial genes homologous to this cluster were identified at a syntenic locus in E. tritici-australis suggesting loss of this cluster. Homologues of Hybrid-2 in other fungi have been proposed to facilitate disease induction in woody plants. Subsequent assays confirmed that E. darliae and E. pseudodarliae were both pathogenic on woody plant hosts, but E. tritici-australis was not, implicating woody plants as potential host reservoirs for the fungi. We hypothesise that loss of the cluster in E. tritici-australis represents a committed lifestyle jump to grasses.\nC_LIO_LICombined, our observations relating to the secondary metabolite potential of the WGD Eutiarosporella spp. have contributed novel data to the field by expanding the range of known fungal secondary metabolite genes, and helped develop our understanding of the lifestyle and potential host-range of a recently emerged pathogen of wheat.\nC_LI

plant biology↗

bioRxiv2018

PET Brain imaging of α7-nAChR with ASEM Reproducibility, occupancy, receptor density, and changes in schizophrenia

The 7 nicotinic acetylcholine receptor (nAChR) increasingly has been implicated in normal brain physiology, as well as in neuropsychiatric disorders. The a7-nAChR primarily is located in cerebral cortex and sub-cortical regions, compared to the 4{beta}2 nAChR subtype that has a more subcortical distribution. The highly cortical distribution suggests a role of a7-nAChR in cognition. We expanded the first-in-human PET imaging of 7-nAChR with [18F]ASEM from five to 21 healthy non-smoking volunteers and added preliminary evidence of binding in six male patients with schizophrenia. Study aims included 1) confirmation of test-retest reproducibility of [18F]ASEM binding in normal volunteers, 2) demonstration of specificity of [18F]ASEM binding by competition with DMXB-A, an 7-nAChR partial agonist previously tested in clinical trials of patients with schizophrenia, 3) estimation of [18F]ASEM binding potentials and 7-nAChR density in vivo in humans, and 4) 7-nAChR binding in patients with schizophrenia compared to healthy volunteers.\n\nTest-retest PET confirmed reproducibility (>90%) (variability [≤] 7%) of [18F]ASEM volume of distribution (VO_SCPLOWTC_SCPLOW) estimates in healthy volunteers. Repeated sessions of PET in five healthy subjects included baseline and effect of inhibition after oral administration of 150 mg DMXB-A. From reduction of binding potentials, we estimated the dose-dependent occupancy of 7-nAChR by DMXB-A at 17-49% for plasma concentrations at 60-200 nM DMXB-A. In agreement with evidence post-mortem, 7-nAChR density (Bmax) averaged 0.67-0.82 nM and inhibitor affinity constant (KO_SCPLOWIC_SCPLOW) averaged 170-385 nM. Median VO_SCPLOWTC_SCPLOW in a feasibility study of six patients with schizophrenia was lower than in healthy volunteers in cingulate cortex, frontal cortex, and hippocampus. Mann-Whitney test identified cingulate cortex and hippocampus as regions with significantly lower median VO_SCPLOWTC_SCPLOW in patients than in healthy volunteers when a single outlier patient was excluded from analysis (P = 0.02, corrected for multiple comparisons).

neuroscience↗

bioRxiv2017

Distribution and inheritance of a gene cluster encoding a sulfated tyrosine peptide in Xanthomonas spp.

The rice XA21-mediated immune response is activated upon recognition of the RaxX peptide produced by the bacterium Xanthomonas oryzae pv. oryzae (Xoo). The 60 residue RaxX precursor is posttranslationally modified to form a sulfated tyrosine peptide that shares sequence and functional similarity with the plant sulfated tyrosine (PSY) peptide hormones. The five kb raxX-raxSTAB gene cluster of Xoo encodes RaxX, the RaxST tyrosylprotein sulfotransferase, and the RaxA and RaxB components of a predicted type one secretion system. The identified the complete raxX-raxSTAB gene cluster is present only in Xanthomonas spp., in five distinct lineages in addition to X. oryzae. The phylogenetic distribution of the raxX-raxSTAB gene cluster is consistent with the occurrence of multiple lateral transfer events during Xanthomonas speciation. RaxX variants representing each of the five lineages, and three Xoo RaxX variants, fail to activate the XA21-mediated immune response yet retain peptide hormone activity. These RaxX variants contain a restricted set of missense mutations, consistent with the hypothesis that selection acts to maintain peptide hormone-like function. These observations are also consistent with the hypothesis that the XA21 receptor evolved specifically to recognize Xoo RaxX.

microbiology↗