Enhanced Expression Levels of Cellulase Enzymes Using Multiple Transcription Units

Transgenic cereals are an attractive option for the accumulation of foreign proteins when large volumes and low cost are required. Previous work has shown maize germ to be a particularly good location for accumulating enzymes that target cellulose for degradation. In this study, recently identified embryo-preferred promoters were used to investigate their ability to increase the accumulation of the enzymes endoglucanase E1 and cellobiohydrolase CBHI. The effect of increasing copy numbers of identical transcription units, as well as multiple copies of the enzyme driven by different promoters, was explored. Results show that accumulation of the E1 or CBHI enzymes can be significantly increased, particularly when using constructs with multiple copies of the transcription units. These findings demonstrate the highest levels of these enzymes obtained in a commercially relevant plant species observed thus far. The methodology described here may provide a low-cost plant-based source of enzymes enabling an economically viable solution for the conversion of cellulose to ethanol.