C. Neal Stewart Jr

Oak Ridge National Laboratory, Oak Ridge, Florida, United States

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Publications (25)67.93 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Transgenic canola (Brassica napus) with a Bacillus thuringiensis cry1Ac gene and a green fluorescent protein (GFP) marker gene was used in hybridization experiments with wild B. juncea. Hybrid F1 and successive five backcross generations were obtained. The pod-set frequency on backcrossed B. juncea plants was over 66%, which suggested relatively high crossing compatibility between the hybrids and wild species. The seed setting in BC1 was the least of all generations tested, and then increased at the BC2 generation for which the thousand-seed weight was the highest of all generations. Seed size in backcrossed generations eventually approached that of the wild parent. The plants in all backcrossed generations were consistent with the expected 1:1 segregation ratio of the transgenes. The Bt Cry1Ac protein concentrations at bolting and flowering stages was higher compared to the 4-5-leaf and pod-formation stages. Nonetheless, the Bt toxin in the fifth backcrossing generation (BC5) was sufficient to kill both polyphagous (Helicoverpa armigera) and oligophagous (Plutella xylostella) Lepidoptera. As a consequence, the subsequent generations harboring the transgene from F1 to BC5 could have selection advantage against insect pests. The result is useful in understanding gene flow from transgenic crops and the followed transgene introgression into wild.
    Plant Science 10/2014; · 4.11 Impact Factor
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    ABSTRACT: The agricultural landscape of the United States could soon be changed by planting of switchgrass (Panicum virgatum L.) cultivars to meet government-mandated targets for lignocellulosic bioenergy production and consumption. This alteration could affect the genetic structure of wild switchgrass populations, which are native to the eastern half of North America through cultivar introgression. In this study, PCR amplification of microsatellite fragments as well as chloroplast gene-specific markers were utilized to quantify the genetic diversity and structure of five native populations and three agronomic fields (hereafter ‘populations’) planted with switchgrass cultivars. Microsatellite polymorphism across all the switchgrass populations ranged from 91.4 to 100 %. Overall, natural switchgrass populations had significantly higher mean genetic diversity than agronomic switchgrass cultivars (0.262 ± 0.102 and 0.201 ± 0.082 respectively, t test p S) and among (HT) as compared to agronomic switchgrass cultivars. A clear separation of natural and agronomic switchgrass populations was noted using principal component analysis and STRUCTURE analysis. A grouping pattern similar to that obtained in the microsatellite study was observed when chloroplast nucleotide sequence variation was assessed. In the realm of bioenergy sustainability, our results highlight the need to consider the genetic structure of cultivars for bioenergy when they are grown in proximity to native switchgrass populations.
    Agroforestry Systems 10/2014; 88(5). · 1.37 Impact Factor
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    ABSTRACT: It is commonly believed that gene duplications provide the raw material for morphological evolution. Both the number of genes and size of gene families have increased during the diversification of land plants. Several small proteins that regulate transcription factors have recently been identified in plants, including the LITTLE ZIPPER (ZPR) proteins. ZPRs are post-translational negative regulators, via heterodimerization, of class III Homeodomain Leucine Zipper (C3HDZ) proteins that play a key role in directing plant form and growth. We show that ZPR genes originated as a duplication of a C3HDZ transcription factor paralog in the common ancestor of euphyllophytes (ferns and seed plants). The ZPRs evolved by degenerative mutations resulting in loss all of the C3HDZ functional domains, except the leucine zipper that modulates dimerization. ZPRs represent a novel regulatory module of the C3HDZ network unique to the euphyllophyte lineage, and their origin correlates to a period of rapid morphological changes and increased complexity in land plants. The origin of the ZPRs illustrates the significance of gene duplications in creating developmental complexity during land plant evolution that likely led to morphological evolution.
    Molecular Phylogenetics and Evolution 09/2014; · 4.07 Impact Factor
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    ABSTRACT: Contamination of ready-to-eat meat products by foodborne pathogens is a major concern in the food industry. Novel methods to control foodborne pathogens are made necessary by continuing outbreaks as well as the development of antibiotic-resistant pathogens. Hibiscus sabdariffa extracts could be useful as a natural source of antimicrobial rinse on ready-to-eat products to control pathogens. In this study, lyophilized Hibiscus flower extracts were examined for their antimicrobial activity as a rinse on all-beef hot dogs against Listeria monocytogenes and methicillin-resistant Staphylococcus aureus (MRSA). Beef hot dogs were dip inoculated in overnight cultures of 1:1 mixtures of L. monocytogenes strains Scott A and 101 or MRSA strains ATCC 33591 and ATCC 33593 and were placed at 4 °C overnight to allow for bacterial attachment. Hot dogs were rinsed with extracts (120, 240 mg/mL) or water (control) for 5, 15, 30, or 60 min and then plated immediately (0 h; no storage) or stored at 4 °C overnight and plated at 24 h. Serial dilutions were plated in duplicate on both TSA and selection media, Modified Oxford (Listeria) or Baird Parker (MRSA), and the entire experiment was replicated 3 times. Higher extract concentrations, longer rinse times, and longer storage times were the most effective at inhibiting and/or killing L. monocytogenes and MRSA on hot dogs. L. monocytogenes was reduced to ca. 1.5 log CFU/g while MRSA was reduced to undetectable levels following rinsing of hot dogs with extracts at 240 mg/mL for 60 min and stored for 24 h. Both L. monocytogenes and MRSA were reduced ca. 2 log CFU/g following rinsing of hot dogs with extracts at 120 mg/mL for 60 min and stored for 24 h. This research demonstrates the effectiveness of Hibiscus extracts against L. monocytogenes and MRSA as an antimicrobial rinse on ready-to-eat meat products.
    Food Control 06/2014; 40:274–277. · 2.74 Impact Factor
  • Wusheng Liu, Joshua S Yuan, C Neal Stewart Jr
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    ABSTRACT: Basic research has provided a much better understanding of the genetic networks and regulatory hierarchies in plants. To meet the challenges of agriculture, we must be able to rapidly translate this knowledge into generating improved plants. Therefore, in this Review, we discuss advanced tools that are currently available for use in plant biotechnology to produce new products in plants and to generate plants with new functions. These tools include synthetic promoters, 'tunable' transcription factors, genome-editing tools and site-specific recombinases. We also review some tools with the potential to enable crop improvement, such as methods for the assembly and synthesis of large DNA molecules, plant transformation with linked multigenes and plant artificial chromosomes. These genetic technologies should be integrated to realize their potential for applications to pressing agricultural and environmental problems.
    Nature Reviews Genetics 10/2013; · 41.06 Impact Factor
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    ABSTRACT: Terahertz absorption signatures from culture-cultivated Bacillus thuringiensis were measured with a THz photomixing spectrometer operating from 400 to 1200 GHz. We observe two distinct signatures centered at ∼955 and 1015 GHz, and attribute them to the optically coupled particle vibrational resonance (surface phonon-polariton) of Bacillus spores. This demonstrates the potential of the THz attenuation signatures as "fingerprints" for label-free biomolecular detection. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).
    Journal of Biophotonics 07/2013; · 3.86 Impact Factor
  • Kellie P. Burris, C. Neal Stewart Jr
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    ABSTRACT: Highlights ► Emphasis on emerging and important foodborne pathogen detection. ► Emphasis on cutting-edge molecular nanotechnologies. ► Emphasis on large-scale, on-the-food detection. ► Futuristic.
    Trends in Food Science & Technology. 12/2012; 28(2):143–152.
  • Kellie P. Burris, C. Neal Stewart Jr
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    ABSTRACT: Highlights ► Emphasis on emerging and important foodborne pathogen detection. ► Emphasis on cutting-edge molecular nanotechnologies. ► Emphasis on large-scale, on-the-food detection. ► Futuristic.
    Trends in Food Science & Technology. 12/2012; 28(2):143–152.
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    Chilean journal of agricultural research. 06/2012; 72(2):268-275.
  • Madhugiri Nageswara-Rao, C. Neal Stewart Jr, Charles Kwit
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    ABSTRACT: Panicum virgatum L. (switchgrass) is an obligate outcrossing C4 perennial prairie grass currently being pursued for the production of lignocellulosic ethanol. Commercial production of switchgrass for bioenergy has increased substantially in the United States. Understanding the degree of native genetic diversity within and among switchgrass populations will facilitate effective germplasm improvement, conservation, and management programs. In this study, the genetic diversity and differentiation among natural and agronomic switchgrass populations were analyzed at the molecular level by using random amplified polymorphic (RAPD) DNA markers. The mean genetic diversity among populations ranged from 0.051 ± 0.136 to 0.243 ± 0.214 and the mean genetic similarity among all the switchgrass populations was 0.775. The clustering pattern of switchgrass populations grouped the individuals based on their sites of origin, with agronomic cultivars predominantly separated into distinct clusters. The grouping of individuals within and across the populations was corroborated by principal component analysis. These results are consistent with previous reports for switchgrass accessions. RAPD DNA markers were suitable for quickly estimating the genetic diversity of native and agronomic switchgrass populations, and suggest that introgression of agronomic genes into natural switchgrass populations and subsequent changes in genetic structure may be detectable.
    Genetic Resources and Crop Evolution 03/2012; 60(3). · 1.59 Impact Factor
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    ABSTRACT: One risk of planting transgenic crops is the escape of transgenes to conspecifics and sexually compatible wild relatives. Detecting transgene escape is thus a crucial biosafety issue world-wide, but most current detection methods are expensive and laborious, as well as being unfeasible for large-scale use in commercial cultivation. We undertook field spectral reflectance studies of non-transgenic oilseed rape (B. napus cv. Westar), a transgenic oilseed rape, Wild Indian mustard (B. juncea var. gracilis) and a hybrid Wild Indian mustard. Simulated reflectances for the spectral bands of several different satellite-flown hyperspectral and multi-spectral scanners were generated. The differences obtained between the simulated reflectances of the different plants leads to the possibility that these differences could be used to detect transgene escape and genomic effects among related taxa from the Moderate Resolution Imaging Spectroradiometer (MODIS) hyperspectral scanner and from the Landsat Thematic Mapper (TM), Satellite Pour l'Observation de la Terre (SPOT) High Resolution Visible (HRV) and IKONOS multi-spectral scanners.
    International Journal of Remote Sensing 02/2011; 32(4):1095-1103. · 1.36 Impact Factor
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    ABSTRACT: Smokey Mountain Smelters in Knoxville, Tennessee USA is an abandoned aluminium smelter where smelter waste (slag) was dumped on site. ICP analyses indicated the highest slag metal concentrations were 223,000 mg kg<sup align="right"> −1 </sup> Al, 281 mg kg<sup align="right"> −1 </sup> As, 132 mg kg<sup align="right"> −1 </sup> Se, and 2910 mg kg<sup align="right"> −1 </sup> Cu. Metal uptake was quantified in plants growing on slag. Our data indicates that P. cretica accumulates Al in high concentrations, but not As, when grown in slag. Metal concentrations in vegetation grown on slag were lower than controls grown in uncontaminated soil, suggesting low metal availability or root exclusion mechanisms.
    Int. J. of Environment and Pollution. 01/2011; 45(4):310 - 326.
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    ABSTRACT: The evolution of glyphosate resistance in weedy species places an environmentally benign herbicide in peril. The first report of a dicot plant with evolved glyphosate resistance was horseweed, which occurred in 2001. Since then, several species have evolved glyphosate resistance and genomic information about nontarget resistance mechanisms in any of them ranges from none to little. Here, we report a study combining iGentifier transcriptome analysis, cDNA sequencing, and a heterologous microarray analysis to explore potential molecular and transcriptomic mechanisms of nontarget glyphosate resistance of horseweed. The results indicate that similar molecular mechanisms might exist for nontarget herbicide resistance across multiple resistant plants from different locations, even though resistance among these resistant plants likely evolved independently and available evidence suggests resistance has evolved at least four separate times. In addition, both the microarray and sequence analyses identified non–target-site resistance candidate genes for follow-on functional genomics analysis. Nomenclature: Glyphosate, horseweed, Conyza canadensis (L.) Cronq. ERICA
    Weed Science 04/2010; · 1.76 Impact Factor
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    ABSTRACT: The genetic basis of weedy and invasive traits and their evolution remain poorly understood, but genomic approaches offer tremendous promise for elucidating these important features of weed biology. However, the genomic tools and resources available for weed research are currently meager compared with those available for many crops. Because genomic methodologies are becoming increasingly accessible and less expensive, the time is ripe for weed scientists to incorporate these methods into their research programs. One example is next-generation sequencing technology, which has the advantage of enhancing the sequencing output from the transcriptome of a weedy plant at a reduced cost. Successful implementation of these approaches will require collaborative efforts that focus resources on common goals and bring together expertise in weed science, molecular biology, plant physiology, and bioinformatics. We outline how these large-scale genomic programs can aid both our understanding of the biology of weedy and invasive plants and our success at managing these species in agriculture. The judicious selection of species for developing weed genomics programs is needed, and we offer up choices, but no Arabidopsis-like model species exists in the world of weeds. We outline the roadmap for creating a powerful synergy of weed science and genomics, given well-placed effort and resources.
    Weed Science 09/2009; · 1.76 Impact Factor
  • Journal of Biotechnology - J BIOTECHNOL. 01/2008; 136.
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    C. Neal Stewart Jr, David W. Ow
    Plant Biotechnology and Genetics: Principles, Techniques, and Applications, 10/2007: pages 357 - 369; , ISBN: 9780470282014
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    Kevin Markham, Tanya Chalk, C. Neal Stewart Jr
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    ABSTRACT: Relatively little is known about insect defense mechanisms in the ferns and mosses. The current paradigm is that secondary metabolites and physical barriers are most important in conferring insect resistance in ferns, lycopods, and mosses. We investigated whether protein-based resistance exists in representatives of these taxa. We screened a total of 23 plant species for protein-based insecticidal activity against the two common lepidopteran pests: corn earworm (Helicoverpa zea) and fall armyworm (Spodoptera frugiperda). Protein extracts from fern and moss species were compared with those from a lepidopteran-susceptible soybean (Glycine max) cultivar (Cobb) in bioassays for insect resistance. The ebony spleenwort (Asplenium platyneuron), sensitive fern (Onoclea sensibilis), glade fern (Anthyrium pycnocarpon), and the burned ground moss (Ceratodon purpureus) protein extracts caused the greatest decrease in damage in leaf-disk assays and insect larval growth. These species are good candidates for follow-up evaluation.
    International Journal of Plant Sciences - INT J PLANT SCI. 01/2006; 167(1):111-117.
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    ABSTRACT: North America. High biomass production and wide adaptation has made switchgrass a leading lignocellulosic feedstock. One of its major limitations is the recalcitrance of complex carbohydrates to hydrolysis for conversion of lignocellulosic biomass into biofuels. Lignin is a primary contributor to recalcitrance as it creates a physical and chemical barrier to enzymatic access of cell wall polysaccharides. Therefore, genetic manipulation of the lignin biosynthetic pathway in an effort to reduce lignin content is a promising approach for overcoming this inherent cell wall recalcitrance. Low-lignin transgenic switchgrass plants were produced via down-regulation of caffeic acid O-methyltransferase (COMT), or by up-regulation of the MYB4 transcription factor, an R2R3 type MYB repressor of the lignin biosynthetic pathway. Resulting COMT transgenic plants exhibited increased ethanol yields by up to 38% compared to the control and required less severe pretreatment and 300-400% less cellulase enzyme loading. Resulting MYB4 overexpression transgenic plants demonstrated 3-fold increase in sugar release efficiency and 2.5-fold increase in ethanol production without pretreatment compared to control; all analyses used greenhouse-grown plants. Field trials of COMT and MYB transgenic switchgrass are underway in Knoxville, Tennessee where plants are assessed during a period of three growing seasons for 1) agronomic biomass performance (tiller height, plant width, tiller number) and biomass yield, 2) cell wall characterization 3) biorefinery performance including pretreatment response, sugar release efficiency, and ethanol yield, and 4) rust disease susceptibility of transgenic plants compared to controls.
    International Plant and Animal Genome Conference XXI 2013;
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    ABSTRACT: Trees in the genus Copaifera produce a sesquiterpene-rich oleoresin that has been used as traditional medicine, food and cosmetics, and even as a biofuel, leading to the common name ‘diesel trees.’ While sesquiterpene biosynthesis is common in plants, these unique trees can produce liters of sesquiterpenes. Investigating the entire sesquiterpene biosynthesis pathway and associated precursor pathways present in Copaifera trees could lead to a greater understanding of this unique phenotype. In specific, it is unclear if these trees respond to biotic stress or wounding by up-regulating terpenoid biosynthesis; or whether the large quantities of sesquiterpenes are a result of specialized storage and/or unique biosynthesis characteristics. Solexa (Illumina) next-generation transcriptome sequencing was performed on mRNA isolated from C. officinalis leaf and stem tissue. Reads were assembled using either the CLC bio genomics or Velvet, and annotated using the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO). Six putative terpene synthase transcripts were identified by BLAST similarity to known sesquiterpene synthases and conserved domain motifs (CDD NCBI), cloned, and expressed in recombinant Escherichia coli for functional characterization. As C. officinalis oleoresin and tissues contain primarily sesquiterpenes, putative mevalonic acid (MVA), sesquiterpene precursor biosynthesis, and 2-C-methyl-D-erythritol 4-phosphate (MEP) transcripts were assembled and transcripts present in tissues were quantified using qPCR. In conclusion, de novo transcriptome sequencing allowed for rapid identification and characterization of genes associated with two metabolic pathways. We can now test hypotheses associated with the entire terpene metabolic pathway in C. officinalis instead of single genes.
    International Plant and Animal Genome Conference XX 2012;
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    ABSTRACT: Ferns are the second most diverse group of land plants composed of 250 genera, occupy an important role in the evolution of gymnosperms and angiosperms. The group lacks any stable transformation method, and this hampers studies of functional genomics. Among ferns, Pteris vittata the only known arsenic hyperaccumulator and model C-ferns are the most studied of the pteridophyte. Our current efforts are focused on the development of stable transformation methods of these two fern species, using native and canonical constitutive promoters that regulate various marker genes such as GUS and fluorescent proteins. These tools will help to develop overexpression and knockdown studies to understand their uniqueness in stress tolerance, pest resistance and allelopathy. These tools will also elucidate to understand ferns’ metabolic, physiological pathways using RNAi studies in their all life stages including haploid gametophyte and diploid sporophyte stages.
    International Plant and Animal Genome Conference XX 2012;

Publication Stats

43 Citations
67.93 Total Impact Points

Institutions

  • 2014
    • Oak Ridge National Laboratory
      Oak Ridge, Florida, United States
  • 2006–2014
    • The University of Tennessee Medical Center at Knoxville
      Knoxville, Tennessee, United States
  • 2013
    • Wright State University
      Dayton, Ohio, United States
  • 2007–2012
    • University of Tennessee
      • Department of Plant Sciences
      Knoxville, Tennessee, United States