A THERMOSTABLE XYLANASE FROM CLOSTRIDIUM-THERMOCELLUM EXPRESSED AT HIGH-LEVELS IN THE APOPLAST OF TRANSGENIC TOBACCO HAS NO DETRIMENTAL EFFECTS AND IS EASILY PURIFIED

We expressed a truncated version of the Clostridium thermocellum xylanase (xynZ) gene in transgenic tobacco plants. High levels of the 37 kD protein were synthesized and correctly targeted to the intercellular space by means of the proteinase inhibitor II signal peptide. The protein was one of the most abundant proteins in total extracts that were not protected against proteolysis. Enzyme extracted from leaves retained its activity and hydrolyzed xylan efficiently to xylo-oligomers and xylose. Enzymatic activity could be enriched about 14 to 31-fold after heat-treatment with essentially complete recovery. The transgenic plants, grown under greenhouse conditions, were not affected by the foreign enzyme, possibly due to the high temperature optimum (70 degrees C) of the xylanase and low levels of xylan in dicotyledons. These plants might be useful for production of the enzyme which has numerous applications in the paper industry and agriculture.