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Authors Smith

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Smith, Grant R.


Publications
6

CitationNamesAbstract
Genetic drift and genome reduction in the plant pathogenCandidatusLiberibacter solanacearum shapes a new enzyme in lysine biosynthesis Gilkes et al. (2023). “Liberibacter solanacearum”
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The First Purification of Functional Proteins from the Unculturable, Genome-Reduced, Bottlenecked α-Proteobacterium ‘Candidatus Liberibacter solanacearum’ Gilkes et al. (2019). Phytopathology® 109 (7) “Liberibacter solanacearum”
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Draft Genome Sequence of a “ Candidatus Liberibacter europaeus” Strain Assembled from Broom Psyllids (Arytainilla spartiophila) from New Zealand Frampton et al. (2018). Genome Announcements 6 (20) Ca. Liberibacter europaeus
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Potential pathogenicity determinants in the genome of ‘Candidatus Liberibacter solanacearum’, the causal agent of zebra chip disease of potato Gilkes et al. (2018). Australasian Plant Pathology 47 (2) “Liberibacter solanacearum”
Genomic sequence of 'Candidatus Liberibacter solanacearum' haplotype C and its comparison with haplotype A and B genomes Wang et al. (2017). PLOS ONE 12 (2) “Liberibacter solanacearum”
Genomes of ‘Candidatus Liberibacter solanacearum’ Haplotype A from New Zealand and the United States Suggest Significant Genome Plasticity in the Species Thompson et al. (2015). Phytopathology® 105 (7) “Liberibacter solanacearum”
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Genetic drift and genome reduction in the plant pathogenCandidatusLiberibacter solanacearum shapes a new enzyme in lysine biosynthesis
AbstractThe effect of population bottlenecks and genome reduction on enzyme function is poorly understood. ‘CandidatusLiberibacter solanacearum’ is a bacterium with a reduced genome that is transmitted vertically to the egg of an infected psyllid—a population bottleneck that imposes genetic drift and is predicted to affect protein structure and function. Here, we define the effects of genome reduction and genetic drift on the function ofCa. L. solanacearum dihydrodipicolinate synthase (CLsoDHDPS), which catalyses the committed branchpoint reaction in diaminopimelate and lysine biosynthesis. We demonstrate thatCLsoDHDPS is expressed inCa. L. solanacearum and expression is increased ∼2-fold in the insect host compared toin planta.CLsoDHDPS has increased aggregation propensity, implying mutations have destabilised the enzyme but are compensated for through elevated chaperone expression and a stabilised oligomeric state.CLsoDHDPS uses a ternary-complex kinetic mechanism, which is unique among DHDPS enzymes, has unusually low catalytic ability, but an unusually high substrate affinity. Structural studies demonstrate that the active site is more open, and the structure ofCLsoDHDPS with both pyruvate and the substrate analogue succinic-semialdehyde reveals that the product is both structurally and energetically different and therefore evolution has in this case fashioned a new enzyme. Our study reveals the effects of genome reduction and genetic drift on the function of essential enzymes and provides insights on bacteria-host co-evolutionary association. We suggest that bacteria with endosymbiotic lifestyles present a rich vein of interesting enzymes useful for understanding enzyme function and/or informing protein engineering efforts.
The First Purification of Functional Proteins from the Unculturable, Genome-Reduced, Bottlenecked α-Proteobacterium ‘Candidatus Liberibacter solanacearum’
‘Candidatus Liberibacter solanacearum’ is an unculturable α-proteobacterium that is the causal agent of zebra chip disease of potato—a major problem in potato-growing areas, because it affects growth and yield. Developing effective treatments for ‘Ca. L. solanacearum’ has been hampered by the difficulty in functionally characterizing the proteins of this organism, largely because they are not easily expressed and purified in standard expression systems. ‘Ca. L. solanacearum’ has a reduced genome and its proteins are predicted to be prone to instability and aggregation. Among intracellular-dwelling bacteria, chaperone proteins are conserved and overexpressed to buffer against problems in protein folding. We mimicked this approach for expressing and purifying ‘Ca. L. solanacearum’ proteins in Escherichia coli by coexpressing them with chaperones. Neither of the representative ‘Ca. L. solanacearum’ enzymes, dihydrodipicolinate synthase (key in lysine biosynthesis) and pyruvate kinase (involved in glycolysis), were overexpressed in standard E. coli expression plasmids or strains. However, soluble dihydrodipicolinate synthase was successfully coexpressed with GroEL/GroES, while soluble pyruvate kinase was successfully coexpressed with either GroEL/GroES, dnaK/dnaJ/grpE, or a trigger factor. Both enzymes, believed to be key proteins for the organism, were purified by a combination of affinity chromatography and size-exclusion chromatography. Additionally, both ‘Ca. L. solanacearum’ enzymes are active and have the canonical tetrameric oligomeric structure in solution, consistent with other bacterial orthologs. This is the first study to successfully isolate and functionally characterize proteins from ‘Ca. L. solanacearum’. Thus, we provide a general strategy for characterizing its proteins, enabling new research and drug discovery programs to study and manage the pathogenicity of the organism.
Draft Genome Sequence of a “ Candidatus Liberibacter europaeus” Strain Assembled from Broom Psyllids (Arytainilla spartiophila) from New Zealand
ABSTRACT Here, we report the draft genome sequence of “ Candidatus Liberibacter europaeus” ASNZ1, assembled from broom psyllids ( Arytainilla spartiophila ) from New Zealand. The assembly comprises 15 contigs, with a total length of 1.33 Mb and a G+C content of 33.5%.
Genomes of ‘Candidatus Liberibacter solanacearum’ Haplotype A from New Zealand and the United States Suggest Significant Genome Plasticity in the Species
‘Candidatus Liberibacter solanacearum’ contains two solanaceous crop-infecting haplotypes, A and B. Two haplotype A draft genomes were assembled and compared with ZC1 (haplotype B), revealing inversion and relocation genomic rearrangements, numerous single-nucleotide polymorphisms, and differences in phage-related regions. Differences in prophage location and sequence were seen both within and between haplotype comparisons. OrthoMCL and BLAST analyses identified 46 putative coding sequences present in haplotype A that were not present in haplotype B. Thirty-eight of these loci were not found in sequences from other Liberibacter spp. Quantitative polymerase chain reaction (qPCR) assays designed to amplify sequences from 15 of these loci were screened against a panel of ‘Ca. L. solanacearum’-positive samples to investigate genetic diversity. Seven of the assays demonstrated within-haplotype diversity; five failed to amplify loci in at least one haplotype A sample while three assays produced amplicons from some haplotype B samples. Eight of the loci assays showed consistent A–B differentiation. Differences in genome arrangements, prophage, and qPCR results suggesting locus diversity within the haplotypes provide more evidence for genetic complexity in this emerging bacterial species.
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