Failure to over-express expansin in multiple heterologous systems

BackgroundExpansin has been proposed to be an enhancer of cellulase activity in the deconstruction of biomass for sugars for industrial applications. However, the expansin protein is present in plant tissue only in minute quantities for promoting growth. Thus, producing adequate amounts of expansin for applications in industry will require a heterologous system that will over-express an expansin gene to produce large quantities of expansin protein. Development of a production system requires a facile, rapid assay. However, because no straightforward assay for expansin protein exists, we attempted to make milligram quantities of the protein in a fast or transient system for anti-expansin antibody preparation for use on Western blots or in ELISA assays.ResultsWe tested the expression of the cucumber expansin gene in several heterologous systems including Escherichia coli and transient Nicotiana benthamiana leaves with limited success. We also had limited success in transiently expressing an alternative expansin gene from bamboo in N. benthamiana leaves. In order to determine if expansin over-expression is limited to a seed system, Arabidopsis thaliana seeds were tested. Although all positive and negative controls behaved as expected, none of these common systems expressed the expansin gene well.ConclusionsOver-expression of cucumber expansin in three heterologous systems, E. coli, transient tobacco leaves, and Arabidopsis seeds was unsuccessful. The cause of this failure is not known. These results confirm the necessity of experimentally exploring several heterologous systems for protein production in order to find one with utility.