Little is known about the extracellular enzymes A. nidulans produces while growing on plant cell wall polysaccharides. This study is based on a novel molecular screening method, aimed at the recovery of cDNA clones from all transcripts A. nidulans induces when forced to shift from glucose to a medium containing one or a range of polysaccharides, including pectin, cellulose, xylan and other plant cell wall components. cDNAs, prepared from mRNA templates extracted from glucose-grown cultures, were labeled (herein designated glucose-grown probes) and used to screen a cDNA plasmid library made from mRNAs extracted from plant cell wall polysaccharide-containing cultures (herein designated polymer-grown library). Isolation of condition-specific induced cDNAs was accomplished through differential DNA/DNA hybridization among a labeled glucose-grown probe, membrane cross-linked polymer-grown plasmid-clone library and negatives were selected for further analysis under the assumption that they were the ones induced as a consequence of the physiological shift. Thus, if selection of negatives is exhaustive, the suggested approach is comprehensive because a whole gene set activated by a specific physiological condition is recovered. We have isolated over 1,600 unique cDNA whose transcript does not appear to be present in glucose growing cultures and observed that only a fraction of polysaccharide degrading enzyme coding genes were found. Moreover, the screening data have been corroborated with time-course microarray expression profiling. This unexpected outcome suggests that significant intracellular metabolic changes take place when shifting carbon sources and that the presence of extracellular polymer degrading activities is regulated differently, not involving an exclusive induction of gene expression.
Fungal Genet. Newsl. 50 (Supl):abstract
Full conference title:
22nd Fungal Genetics Conference
- Fungal Genetics Conference 22nd (2001)