C. Neal Stewart Jr

The University of Tennessee Medical Center at Knoxville, Knoxville, Tennessee, United States

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Publications (32)103.83 Total impact

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    Yongbo Liu · Junsheng Li · C. Neal Stewart Jr · Zunlan Luo · Nengwen Xiao
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    ABSTRACT: The adventitious presence of transgenic crops in wild plant populations is of ecological and regulatory concern. In this context, their effects on non-target, below-ground organisms are not well understood. Here, we introduced, at various frequencies, Bt-transgenic oilseed rape (OSR, Brassica napus) into wild mustard (Brassica juncea) populations in the presence and absence of the target herbivore (Plutella xylostella). The impacts on soil nematode and microbial communities were assessed in this system. There were no significant changes on the number of nematode genera and abundance in proportions of OSR with mustard. Nonetheless, the Shannon-Wiener and Pielou evenness index was lowest in plant stands containing 50% of Bt-transgenic OSR. Among treatments, there was no significant variation for culturable soil microbes. There was a positive association between foliar herbivory and the abundance of plant parasitic (PP) and cp-3 nematodes, whereas there was no association between herbivory and soil microbial populations. There was no direct effects of the presence of Bt-transgenic OSR in wild mustard populations on the rhizosphere nematode and microbial communities, whereas its indirect effects via aboveground herbivory might be important to consider for biosafety assessments. Copyright © 2015 Elsevier B.V. All rights reserved.
    Science of The Total Environment 10/2015; 530. DOI:10.1016/j.scitotenv.2015.05.073 · 4.10 Impact Factor
  • Wusheng Liu · C. Neal Stewart Jr
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    ABSTRACT: Plant synthetic biology is an emerging field that combines engineering principles with plant biology toward the design and production of new devices. This emerging field should play an important role in future agriculture for traditional crop improvement, but also in enabling novel bioproduction in plants. In this review we discuss the design cycles of synthetic biology as well as key engineering principles, genetic parts, and computational tools that can be utilized in plant synthetic biology. Some pioneering examples are offered as a demonstration of how synthetic biology can be used to modify plants for specific purposes. These include synthetic sensors, synthetic metabolic pathways, and synthetic genomes. We also speculate about the future of synthetic biology of plants. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Trends in Plant Science 03/2015; 20(5). DOI:10.1016/j.tplants.2015.02.004 · 13.48 Impact Factor
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    Hao Ji · Yanhui Peng · Nicole Meckes · Sara Allen · C. Neal Stewart Jr · M. Brian Traw
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    Hao Ji · Yanhui Peng · Nicole Meckes · Sara Allen · C. Neal Stewart Jr · M. Brian Traw
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    ABSTRACT: Plants have been shown previously to perceive bacteria on the leaf surface and respond by closing their stomata. The virulent bacterial pathogen, Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), responds by secreting a virulence factor, coronatine, which blocks the functioning of guard cells and forces stomata to reopen. Once inside the leaf, Pst DC3000 has been shown to upregulate ABA signaling and thereby suppress SA-dependent resistance. Some wild plants exhibit resistance to Pst DC3000, but the mechanisms by which they achieve this resistance remain unknown. Here, we use genome-wide association mapping to identify an ATP-dependent binding cassette transporter gene, AtABCG16, in Arabidopsis thaliana that contributes to wild plant resistance to Pst DC3000. Through microarray analysis and GUS reporter lines, we show that the gene is upregulated by ABA, bacterial infection, and coronatine. We also use a GFP-fusion protein and find that transporter is more likely to localize on plasma membrane than in cell walls. T-DNA insertion lines exhibited consistent defective tolerance of exogenous ABA and reduced resistance to infection by Pst DC3000. Our conclusion is that AtABCG16 is involved in ABA tolerance and contributes to plant resistance against Pst DC3000. This is one of the first examples of ABC transporter involvement in plant resistance to infection by a bacterial pathogen. It also suggests a possible mechanism by which plants reduce the deleterious effects of ABA hijacking during pathogen attack. Collectively, these results improve our understanding of basal resistance in Arabidopsis and offer novel ABA-related targets for improving the innate resistance of plants to bacterial infection.
  • Di Cao · C. Neal Stewart Jr · Min Zheng · Zhengjun Guan · Zhi-xi Tang · Wei Wei · Ke-ping Ma
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    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; 227. DOI:10.1016/j.plantsci.2014.06.018 · 4.11 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 10/2014; 7(10). DOI:10.1002/jbio.201300042 · 3.86 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). DOI:10.1007/s10457-014-9728-z · 1.24 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; 81. DOI:10.1016/j.ympev.2014.06.017 · 4.02 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(1):274–277. DOI:10.1016/j.foodcont.2013.12.011 · 2.82 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; 14(11). DOI:10.1038/nrg3583 · 39.79 Impact Factor
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    ABSTRACT: The evolutionary significance of introgression has been discussed for decades. Questions about potential impacts of transgene flow into wild and weedy populations brought renewed attention to the introgression of crop alleles into those populations. In the past two decades, the field has advanced with considerable descriptive, experimental, and theoretical activity on the dynamics of crop gene introgression and its consequences. As illustrated by five case studies employing an array of different approaches, introgression of crop alleles has occurred for a wide array of species, sometimes without significant consequence, but on occasion leading to the evolution of increased weediness. A new theoretical context has emerged for analyzing empirical data, identifying factors that influence introgression, and predicting introgression’s progress. With emerging molecular techniques and analyses, research on crop allele introgression into wild and weedy populations is positioned to make contributions to both transgene risk assessment and reticulate evolution.
    Annual Review of Ecology Evolution and Systematics 09/2013; 44(12):1-17. DOI:10.1146/annurev-ecolsys-110512-135840 · 10.98 Impact Factor
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    ABSTRACT: As a native, low-input crop with high biomass production, switchgrass (Panicum virgatum) has become a favorable feedstock for the production of cellulosic biofuels in the United States. Many efforts are being made to improve the production of cellulosic biofuels from switchgrass. Protocols regarding analysis of switchgrass biomass have been established; however, the developmental stage of the materials being analyzed has varied depending on researchers’ discretion, and no standardized harvesting procedure has been defined. Developmental stages have a large impact on the results of biochemical analyses. We propose a standardized procedure for switchgrass sample collection for cell wall and biomass analyses by describing various developmental stages of switchgrass, defining the R1 stage as the stage at which tillers should be collected, and providing a detailed description of how and what material should be analyzed. Such a standardized procedure will help to maintain consistency in switchgrass evaluation methods, enable comparisons of data obtained from different approaches and studies, and facilitate efforts towards improving switchgrass as a bioenergy crop.
    BioEnergy Research 06/2013; 6(2). DOI:10.1007/s12155-012-9292-1 · 3.40 Impact Factor
  • Kellie P. Burris · C. Neal Stewart Jr
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    ABSTRACT: Emerging tools in molecular nanotechnology will be useful to monitor and quantify pathogen levels and toxin production inter-and intra-cellularly and on the surface of foods. Recent developments in the manufacture and modification of fluorescent nanoparticles, quantum dots (QD), in conjunction with established molecular beacon (MB) technology, have demonstrated potential for on-the-food detection and quantification of pathogens and toxins harmful to human health. Recent research has demonstrated QDs effective use for in vivo cellular imaging, demonstrating its potential use in detecting live bacterial contamination in foods and crops. We envisage food protection systems using automated sampling of food products with near instantaneous detection and reporting of food contaminants using molecular nanotechnologies. We also address the potential limitations of these emerging technologies and how shortcomings can be addressed.
    Trends in Food Science & Technology 12/2012; 28(2):143–152. DOI:10.1016/j.tifs.2012.06.013 · 4.65 Impact Factor
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    06/2012; 72(2):268-275. DOI:10.4067/S0718-58392012000200016
  • 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). DOI:10.1007/s10722-012-9903-x · 1.48 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. DOI:10.1080/01431160903505336 · 1.65 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.
    International Journal of Environment and Pollution 01/2011; 45(4):310 - 326. DOI:10.1504/IJEP.2011.040277 · 0.30 Impact Factor
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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; 58(April-June 2010):109-117. DOI:10.1614/WS-D-09-00037.1 · 1.68 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; 57(Sep 2009):451-462. DOI:10.1614/WS-09-011.1 · 1.68 Impact Factor
  • Journal of Biotechnology 10/2008; 136. DOI:10.1016/j.jbiotec.2008.07.585 · 2.88 Impact Factor