Philip A. Lessard, Agrivida, Inc., 200 Boston Ave., Suite 3100, Medford, MA 02155
In planta expression of cell wall degrading (CWD) hydrolases promises to be a cost-effective strategy for producing enzymes that are required for converting biomass to fermentable components. Embedding such enzymes in the plant material as the plant grows could also enable more efficient processing of biomass by initiating hydrolysis of plant polysaccharides with lower restrictions from mass transfer effects, reducing or potentially eliminating the need for exogenous enzymes. Unfortunately, when expressed in transgenic plants, many CWD enzymes cause severe negative phenotypes such as stunting and poor seed set, presumably because their hydrolytic activity interferes with cell wall formation during normal plant development. One option to overcome this barrier to in planta expression has been to generate transgenics in which the CWD enzymes are sequestered into subcellular compartments, away from their natural substrates. An alternative strategy to overcome this problem is to express the CWD enzymes as inactive precursors, which can then be activated post-harvest via any of a number of possible inducers. Thus, enzyme production can be decoupled from hydrolysis, enabling even higher levels of expression in energy crops. We are developing a number of such CWD pro-enzymes for expression in maize, sorghum, and switchgrass, and we are assessing their performance in transgenic plants.
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