Transgenic barley expressing a fungal xylanase gene in the endosperm of the developing grains
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The feasibility of producing plant cell wall polysaccharide-hydrolysing feed enzymes in the endosperm of barley grain was investigated. The coding region of a modified xylanase gene (xynA) from the rumen fungus, Neocallimastix patriciarum, linked with an endosperm-specific promoter from cereal storage protein genes was introduced into barley by Agrobacterium-mediated transformation. Twenty-four independently transformed barley lines with the xylanase gene were produced and analysed. The fungal xylanase was produced in the developing endosperm under the control of either the rice glutelin B-1 (GluB-1) or barley B1 hordein (Hor2-4) promoter. The rice GluB-1 promoter provided an apparently higher expression level of recombinant proteins in barley grain than the barley Hor2-4 promoter in both transient and stable expression experiments. In particular, the mean value for the fungal xylanase activity driven by the GluB-1 promoter in the mature grains of transgenic barley was more than twice that with the Hor2-4 promoter. Expression of the xylanase transgene under these endosperm-specific promoters was not observed in the leaf, stem and root tissues. Accumulation of the fungal xylanase in the developing grains of transgenic barley followed the pattern of storage protein deposition. The xylanase was stably maintained in the grain during grain maturation and desiccation and post-harvest storage. These results indicate that the cereal grain expression system may provide an economic means for large scale production of feed enzymes in the future.
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