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Willis JD, Grant JN, Mazarei M, Kline LM, Rempe CS, Collins AG, Turner GB, Decker SR, Sykes RW, Davis MF, Labbe N, Jurat-Fuentes JL, Stewart CN. The TcEG1 beetle ( Tribolium castaneum) cellulase produced in transgenic switchgrass is active at alkaline pH and auto-hydrolyzes biomass for increased cellobiose release. BIOTECHNOLOGY FOR BIOFUELS 2017; 10:230. [PMID: 29213306 PMCID: PMC5707894 DOI: 10.1186/s13068-017-0918-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Accepted: 09/28/2017] [Indexed: 05/17/2023]
Abstract
BACKGROUND Genetically engineered biofuel crops, such as switchgrass (Panicum virgatum L.), that produce their own cell wall-digesting cellulase enzymes would reduce costs of cellulosic biofuel production. To date, non-bioenergy plant models have been used in nearly all studies assessing the synthesis and activity of plant-produced fungal and bacterial cellulases. One potential source for cellulolytic enzyme genes is herbivorous insects adapted to digest plant cell walls. Here we examine the potential of transgenic switchgrass-produced TcEG1 cellulase from Tribolium castaneum (red flour beetle). This enzyme, when overproduced in Escherichia coli and Saccharomyces cerevisiae, efficiently digests cellulose at optima of 50 °C and pH 12.0. RESULTS TcEG1 that was produced in green transgenic switchgrass tissue had a range of endoglucanase activity of 0.16-0.05 units (µM glucose release/min/mg) at 50 °C and pH 12.0. TcEG1 activity from air-dried leaves was unchanged from that from green tissue, but when tissue was dried in a desiccant oven (46 °C), specific enzyme activity decreased by 60%. When transgenic biomass was "dropped-in" into an alkaline buffer (pH 12.0) and allowed to incubate at 50 °C, cellobiose release was increased up to 77% over non-transgenic biomass. Saccharification was increased in one transgenic event by 28%, which had a concurrent decrease in lignin content of 9%. Histological analysis revealed an increase in cell wall thickness with no change to cell area or perimeter. Transgenic plants produced more, albeit narrower, tillers with equivalent dry biomass as the control. CONCLUSIONS This work describes the first study in which an insect cellulase has been produced in transgenic plants; in this case, the dedicated bioenergy crop switchgrass. Switchgrass overexpressing the TcEG1 gene appeared to be morphologically similar to its non-transgenic control and produced equivalent dry biomass. Therefore, we propose TcEG1 transgenics could be bred with other transgenic germplasm (e.g., low-lignin lines) to yield new switchgrass with synergistically reduced recalcitrance to biofuel production. In addition, transgenes for other cell wall degrading enzymes may be stacked with TcEG1 in switchgrass to yield complementary cell wall digestion features and complete auto-hydrolysis.
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Affiliation(s)
- Jonathan D. Willis
- Department of Plant Sciences, University of Tennessee, Knoxville, TN 37996 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Joshua N. Grant
- Department of Plant Sciences, University of Tennessee, Knoxville, TN 37996 USA
| | - Mitra Mazarei
- Department of Plant Sciences, University of Tennessee, Knoxville, TN 37996 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Lindsey M. Kline
- Center for Renewable Carbon, University of Tennessee, Knoxville, TN 37996 USA
| | - Caroline S. Rempe
- Department of Plant Sciences, University of Tennessee, Knoxville, TN 37996 USA
- UT-ORNL Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN 37996 USA
| | - A. Grace Collins
- Department of Plant Sciences, University of Tennessee, Knoxville, TN 37996 USA
| | - Geoffrey B. Turner
- The National Research Energy Laboratory, Golden, CO 80401 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Stephen R. Decker
- The National Research Energy Laboratory, Golden, CO 80401 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Robert W. Sykes
- The National Research Energy Laboratory, Golden, CO 80401 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Mark F. Davis
- The National Research Energy Laboratory, Golden, CO 80401 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Nicole Labbe
- Center for Renewable Carbon, University of Tennessee, Knoxville, TN 37996 USA
| | - Juan L. Jurat-Fuentes
- Department of Entomology and Plant Pathology, University of Tennessee, Knoxville, TN 37996 USA
| | - C. Neal Stewart
- Department of Plant Sciences, University of Tennessee, Knoxville, TN 37996 USA
- UT-ORNL Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN 37996 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
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Park SH, Ong RG, Sticklen M. Strategies for the production of cell wall-deconstructing enzymes in lignocellulosic biomass and their utilization for biofuel production. PLANT BIOTECHNOLOGY JOURNAL 2016; 14:1329-44. [PMID: 26627868 PMCID: PMC5063159 DOI: 10.1111/pbi.12505] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Revised: 10/23/2015] [Accepted: 11/02/2015] [Indexed: 05/18/2023]
Abstract
Microbial cell wall-deconstructing enzymes are widely used in the food, wine, pulp and paper, textile, and detergent industries and will be heavily utilized by cellulosic biorefineries in the production of fuels and chemicals. Due to their ability to use freely available solar energy, genetically engineered bioenergy crops provide an attractive alternative to microbial bioreactors for the production of cell wall-deconstructing enzymes. This review article summarizes the efforts made within the last decade on the production of cell wall-deconstructing enzymes in planta for use in the deconstruction of lignocellulosic biomass. A number of strategies have been employed to increase enzyme yields and limit negative impacts on plant growth and development including targeting heterologous enzymes into specific subcellular compartments using signal peptides, using tissue-specific or inducible promoters to limit the expression of enzymes to certain portions of the plant or certain times, and fusion of amplification sequences upstream of the coding region to enhance expression. We also summarize methods that have been used to access and maintain activity of plant-generated enzymes when used in conjunction with thermochemical pretreatments for the production of lignocellulosic biofuels.
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Affiliation(s)
- Sang-Hyuck Park
- Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, MI, USA
| | - Rebecca Garlock Ong
- Department of Chemical Engineering and Materials Science, DOE Great Lakes Bioenergy Research Center, Michigan State University, Lansing, MI, USA
- Department of Chemical Engineering, Michigan Technological University, Houghton, MI, USA
| | - Mariam Sticklen
- Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, MI, USA
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Willis JD, Mazarei M, Stewart CN. Transgenic Plant-Produced Hydrolytic Enzymes and the Potential of Insect Gut-Derived Hydrolases for Biofuels. FRONTIERS IN PLANT SCIENCE 2016; 7:675. [PMID: 27303411 PMCID: PMC4885837 DOI: 10.3389/fpls.2016.00675] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Accepted: 05/02/2016] [Indexed: 05/25/2023]
Abstract
Various perennial C4 grass species have tremendous potential for use as lignocellulosic biofuel feedstocks. Currently available grasses require costly pre-treatment and exogenous hydrolytic enzyme application to break down complex cell wall polymers into sugars that can then be fermented into ethanol. It has long been hypothesized that engineered feedstock production of cell wall degrading (CWD) enzymes would be an efficient production platform for of exogenous hydrolytic enzymes. Most research has focused on plant overexpression of CWD enzyme-coding genes from free-living bacteria and fungi that naturally break down plant cell walls. Recently, it has been found that insect digestive tracts harbor novel sources of lignocellulolytic biocatalysts that might be exploited for biofuel production. These CWD enzyme genes can be located in the insect genomes or in symbiotic microbes. When CWD genes are transformed into plants, negative pleiotropic effects are possible such as unintended cell wall digestion. The use of codon optimization along with organelle and tissue specific targeting improves CWD enzyme yields. The literature teaches several important lessons on strategic deployment of CWD genes in transgenic plants, which is the focus of this review.
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Affiliation(s)
- Jonathan D. Willis
- Department of Plant Sciences, University of TennesseeKnoxville, TN, USA
- Oak Ridge National Laboratory, BioEnergy Science CenterOak Ridge, TN, USA
| | - Mitra Mazarei
- Department of Plant Sciences, University of TennesseeKnoxville, TN, USA
- Oak Ridge National Laboratory, BioEnergy Science CenterOak Ridge, TN, USA
| | - C. Neal Stewart
- Department of Plant Sciences, University of TennesseeKnoxville, TN, USA
- Oak Ridge National Laboratory, BioEnergy Science CenterOak Ridge, TN, USA
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