Microbial cell wall-degrading enzymes expression in maize seeds as a potential source for cellulosic ethanol production

Identifier:  TFG:1641

Handle: https://hdl.handle.net/20.500.11797/TFG1641

Authors:  Àvila Cabré, Sílvia

Abstract:
Cell wall-degrading (CWD) enzymes are essential for biorefineries in the production of cellulosic ethanol. However, its production by microbial bioreactors is expected to be high. This is the reason why it has been propounded to use plants as alternative production systems. Corn is known to be a very widespread crop and can produce large quantities of heterologous proteins within low production costs, a fact that makes it perfect for this application. Lignocellulosic biomass requires aggressive thermochemical pretreatments before the enzymatic hydrolysis in order to obtain fermentable sugars. It is necessary for the enzymes which are expressed in this biomass to be thermostable and to display optimum temperature and pH properties similar to those applied in the pretreatments, in order to maintain its enzymatic activity. Maize seeds are considered as one of the bests locations of the plant to express and accumulate enzymes in large amounts almost without affecting its phenotype, and they can be used directly as enzyme-containing biomass in the bioethanol production process. This work summarizes the efforts made within the last twelve years on the production of cell wall-degrading enzymes in transgenic maize seed for use in the deconstruction of lignocellulosic biomass. Some strategies have been employed to increase enzyme yields and reduce negative impacts on plant growth and development. Among others, the following have been included: targeting heterologous enzymes into specific subcellular compartments, using tissue-specific or inducible promoters, modifying the enzymes by the incorporation of inteins in order to nullify its enzymatic activity during the plant’s development period, adding multiple copies of identical transcription units in the constructions, self-pollinations or outcrosses to high-oil lines.