![]() ![]() ![]() Although various plant expression systems have been established as bioreactors, the wider use of plant-derived pharmaceuticals has been limited by low yields due to the dozens of important parameters critically reviewed by Egelkrout et al. Similar methods have also made it possible to use plants as bioreactors for economic production of pharmaceuticals. A wide variety of commercial crops with important agronomic traits have already been produced successfully. Plant biotechnology has great potential to speed up crop improvement and meet the needs of a growing world population. The method described here provides an effective approach to robustly enhance the expression of heterogenous transgenes through copy number manipulation in rice. The use of weak promoter derived selectable markers leads to a high T-DNA copy number and then greatly increases the expression of the foreign gene. The correlation between attenuated selection by a weak promoter and elevation of copy number and foreign gene expression was confirmed by using another relatively weak promoter from nopaline synthase (Nos). However, in the resistant calli and regenerated transgenic plants selected by the use of tCUP1, the constitutive expression of green fluorescent protein (GFP) was dramatically increased as a result of the additive effect of multiple T-DNA insertions. The tCUP1 promoter allowed the recovery of transformed rice plants and conferred tissue specific expression of the GUS reporter, but was much weaker than the CaMV 35S promoter in driving a selectable marker for growth of resistant calli. tCUP1, a fragment derived from the tobacco cryptic promoter (tCUP), was tested for its activity in rice by fusion to both a β-glucuronidase (GUS) reporter and a hygromycin phosphotransferase (HPT) selectable marker. In this study, we report a method to magnify the effect of a single promoter by using a weak promoter-based selection system in transgenic rice. Although many such promoters have been identified and characterized, the increase obtainable from a single promoter is ultimately limited to a certain extent. The conventional way to increase the yield of desired transgenic products is to use strong promoters to control the expression of the transgene. Techniques that enable high levels of transgene expression in plants are attractive for the commercial production of plant-made recombinant pharmaceutical proteins or other gene transfer related strategies. ![]()
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