Cloning of multiple cellulase cDNAs from Volvariella volvacea and their differential expression during substrate colonization and fruiting

We used PCR-based methods to clone and sequence four previously unidentified cellulase cDNAs: cbhI-I, cbhI-II, cbhII-I and egII. CbhI-I, cbhI-II and cbhII-I consist of 1710, 1610 and 1453 bp, respectively, and encode for 512, 458 and 442 amino acids, respectively. EgII consists of 1180bp encoding for 310 amino acids, and belongs to family 61 of the glycosyl hydrolases. CbhI-I, cbhII-I and egII all have a modular structure, with the catalytic domain (CD) and cellulose-binding domain (CBD) located at the C-terminus in cbhI-I and egII, and at the N-terminus in cbhII-I. CbhI-II shows high homology to cbhI-I but lacks a CBD. Northern blotting revealed that cbhI-I, cbhI-II and cbhII-I were coordinately expressed at various stages of the mushroom developmental cycle (substrate colonization to mature fruit body), although the number of cbhI-I transcripts was much smaller. No egII expression was detectable during the substrate colonization phase but transcription levels increased as fruit body morphogenesis progressed.