Molecular cloning and expression analysis of two distinct beta-glucosidase genes, bg1 and aven1, with very different biological roles from the thermophilic, saprophytic fungus Talaromyces emersonii.
Recent sequencing of a number of fungal genomes has revealed the presence of multiple putative beta-glucosidases. Here, we report the cloning of two beta-glucosidase genes (bg1 and aven1), which have very different biological functions and represent two of a number of beta-glucosidases from Talaromyces emersonii. The bg1 gene, encoding a putative intracellular beta-glucosidase, shows significant similarity to other fungal glucosidases from glycosyl hydrolase family 1, known to be involved in cellulose degradation. Solka floc, methyl-xylose, gentiobiose, beech wood xylan, and lactose induced expression of bg1, whereas glucose repressed expression. A second beta-glucosidase gene isolated from T. emersonii, aven1, encodes a putative avenacinase, an enzyme that deglucosylates the anti-fungal saponin, avenacin, rendering it less toxic to the fungus. This gene displays high homology with other fungal saponin-hydrolysing enzymes and beta-glucosidases within GH3. A putative secretory signal peptide of 21 amino acids was identified at the N-terminus of the predicted aven1 protein sequence suggesting that this enzyme is extracellular. Furthermore, T. emersonii cultivated on oat plant biomass was shown to deglucosylate avenacin. The presence of the avenacinase transcript was confirmed by RT-PCR on RNA extracted from mycelia grown in the presence of avenacin. The expression pattern of aven1 on various carbon sources was distinctly different from that of bg1. Only methyl-xylose and gentiobiose induced transcription of aven1. Gentiobiose induces synthesis of a number of cellulase genes by T. emersonii and it may be a possible candidate for the natural cellulase inducer observed in Penicillium purpurogenum. This work represents the first report of an avenacinase gene from a thermophilic, saprophytic fungal source, and suggests that this gene is not exclusive to plant pathogens.
Department of Biochemistry, National University of Ireland, Galway, Ireland.
Catherine M
CM
Collins
Patrick G
PG
Murray
Stuart
S
Denman
John P
JP
Morrissey
Lucy
L
Byrnes
Tuula T
TT
Teeri
Maria G
MG
Tuohy
D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D003470:Culture Media; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D006358:Hot Temperature; D008969:Molecular Sequence Data; D012503:Saponins / Q000378:metabolism; D017422:Sequence Analysis, DNA; D032901:Talaromyces / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D001617:beta-Glucosidase / Q000737:chemistry / Q000145:classification* / Q000235:genetics / Q000378:metabolism*
D003470:Culture Media; D005656:Fungal Proteins; D012503:Saponins; C091460:avenacin A 1; D001617:beta-Glucosidase