Regulation of xyn3 gene expression in Trichoderma reesei PC-3-7

The characteristics of regulation of the gene encoding the third xylanase ( Xyn III) of a filamentous fungus, Trichoderma reesei PC-3-7, were studied b y Northern blot analysis. A partial DNA sequence (185 bp) of the xyn3 gene was obtained by PCR amplification of genomic DNA of T. reesei PC-3-7 and se quenced. This xyn3 gene fragment was used as a probe for Southern and North ern blot analysis. The expression of the xyn3 gene was regulated at the tra nscriptional level. The xyn3 mRNA was expressed in mycelia of T. reesei PC- 3-7 induced by Avicel, L-sorbose and sophorose, but not by xylose, xyloolig osaccharides and birchwood xylan. Furthermore, it was observed that xyn3 wa s synchronously expressed with egl1 but not with xyn1 and xyn2 by L-sorbose , indicating that the xyn3 gene may be coordinately expressed with cellulas e genes. By Southern blot analysis, the xyn3 gene was confirmed to exist as a single copy in both strains of T. reesei PC-3-7 and QM9414. However, no xyn3 mRNA appeared in the mycelia induced by any kind of inducers in T. ree sei QM9414 even when total RNA was used in large excess, suggesting that th e xyn3 gene in T. reesei QM9414 is in the dormant state and cannot be expre ssed. Therefore, T. reesei PC-3-7 may be a very useful strain for elucidati ng the induction mechanism of xylanase biosynthesis by cellulosic and xylan osic substrates, and also the regulatory correlation between cellulase and xylanase induction.