Release of xylanase from conidia and germlings of Blumeria graminis f. sp. tritici and expression of a xylanase gene

 Expression of a xylanase gene and release of xylanases by Blumeria graminis were investigated. Exudates released from ungerminated conidia and germlings on plastic membranes were collected and fractionated through anion- and cation-exchange columns. Xylanase activity was detected in the exudate of both ungerminated conidia and germlings by a p-nitrophenyl-d-xylopyranoside (PNPX) assay, and the fractions were eluted stepwise by 0.2–0.5 M NaCl from an anion-exchange column by a plate assay. The activity detected in the fractions eluted by 0.2 and 0.3 M NaCl from an anion-exchange column by a PNPX assay increased during morphogenesis on the membranes. Genomic Southern blot analysis with a heterologous probe prepared from Aspergillus oryzae xynG1 demonstrated the existence of multiple xylanase genes in the genome of this fungus. Using this probe, one xylanase gene, xyn1, was cloned from its genomic library. The nucleotide and predicted amino acid sequences showed high homology to those of endo-1,4-β-xylanases produced by other fungi. The reverse transcription-polymerase chain reaction showed that xyn1 expression increased in ungerminated conidia and germlings with the time after inoculation onto plastic membranes.