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 xylan ase (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 prot ein was one of the most abundant proteins in total extracts that were not protected against proteolysis. Enzyme extracted from leaves retain ed its activity and hydrolyzed xylan efficiently to xylo-oligomers and xylose. Enzymatic activity could be enriched about 14 to 31-fold afte r heat-treatment with essentially complete recovery. The transgenic pl ants, grown under greenhouse conditions, were not affected by the fore ign enzyme, possibly due to the high temperature optimum (70 degrees C ) of the xylanase and low levels of xylan in dicotyledons. These plant s might be useful for production of the enzyme which has numerous appl ications in the paper industry and agriculture.