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Renewables > BioenergyGenetic Engineering of Cellulose Accumulation
Start Date: April 2005
The goal is to express the three CESA genes (CESA4, 7, 8) that make secondary cell wall cellulose in cells that do not normally have secondary wall thickening. Because it is likely to be deleterious to induce extra cellulose synthesis in cells that need to divide and expand to support normal growth and development, the genes must be placed under transcriptional control of a promoter that is active at a time that is compatible with normal development. We will approach this technical issue in two ways. First we will use a chemically inducible promoter (dexamethasone or a similar promoter) so that we can induce transcription by exogenous application of an inducing chemical. This technique will allow production and propagation of the transgenic plants and will also facilitate studies of the consequences of inducing expression of the CESA genes at specific times and places and to different degrees.
If increased cellulose is obtained from chemical induction of the genes, we will test the feasibility of engineering enhanced cellulose under the control of developmental stage-specific promoters. The purpose of this experiment is to determine the effects on growth and development of increasing cellulose deposition in mature cells. Such plants may also allow the formulation of expectations for increased cellulose production in energy crops based on similar strategies.
The transgenic plants containing the ectopic CESA genes will be analyzed for cell wall composition (e.g., cellulose and other polymers) and for effects on growth and development. Additionally, in order to examine whether the transgenic plants sense and respond to the abnormal expression of the CESA genes we will examine effects on gene expression using whole genome DNA chips.
If the experiments described above are promising, it would be useful to proceed directly to implementation in an advanced switchgrass cultivar. In order to implement the approach in switchgrass, it will almost certainly be possible to use the Arabidopsis cellulose synthase genes. By contrast, it will probably not be possible to use the same promoters. Therefore, if time permits and preliminary results with Arabidopsis are promising, we will begin work on identification of a suitable promoter from switchgrass that could be used to induce secondary cellulose deposition.
1. Turner S. and Somerville C. (1997). Collapsed xylem phenotype of Arabidopsis identifies mutants deficient in cellulose deposition in the secondary cell wall. Plant Cell 9, 689-701.
2. Scheible W.R., Eshed R., Richmond T., Delmer D. and Somerville C. (2001). Modifications of cellulosesynthase confer resistance to isoxaben and thiazolidinone herbicides in Arabidopsis Ixr1 mutants. Proc.Natl. Acad. Sci. USA 98, 10079-10084.
3. Taylor N., Howells R., Huttly A., Vickers K. and Turner S. (2003). Interactions among three distinct CesA proteins essential for cellulose synthesis. Proc. Natl. Acad. SCI. USA, 100, 1450-1455.
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