Transcriptomic analysis of the exit from dormancy of Aspergillus fumigatus conidia

Abstract

Background: Establishment of aspergillosis is depending upon the exit from dormancy and germination of the conidia of Aspergillus fumigatus in the lung. To gain an understanding of the molecular mechanisms underlying the early steps of conidial germination, we undertook a transcriptomic analysis using macroarrays constructed with PCR fragments from > 3,000 genes (around one third of the annotated A. fumigatus genome).

Results: Major results of this analysis are the following: (i) conidia stored pre-packaged mRNAs transcripts (27% of genes have transcripts in the resting conidia; (ii) incubation at 37 degrees C in a nutritive medium induced up- and down-regulation of genes: 19% of the total number of genes deposited on the array were up-regulated whereas 22% of the genes with pre-packaged mRNA in the resting conidia were down-regulated; (iii) most modifications were seen during the first 30 min of germination whereas very little modification of gene expression occurred during the following hour; (iv) one-year old conidia and one-week old conidia behaved similarly at transcriptional level.

Conclusion: Transcriptomic data indicate that the exit from dormancy is associated with a shift from a fermentative metabolism to a respiratory metabolism as well as a trend toward immediate protein synthesis.

Figure 1

Germination kinetics of one-week and one-year old conidia. Swelling of the conidia and germ tube formation is computed. Agglutination of swollen conidia and first doubling of the nucleus is shown by an arrow.

Figure 2

Putative molecular function or biological process (matched to the Gene Ontology) of genes with an active transcripts in dormant one-week and one-year old conidia. Histogram indicated the total number of genes of the GO category deposited on the membrane, and the curve the percentage of genes per GO category with transcript stored in the resting conidia.

Figure 3

Putative molecular function or biological process (as GO terms) of genes up- and down-regulated during the first 30 min germination of young conidia. Modulated expression of up-regulated genes = number of up-regulated genes/total number of genes deposited on the array × 100; modulated expression of down-regulated genes = number of down-regulated genes/total number of genes with an active transcript at T0 × 100.

Figure 4

Putative molecular function or biological process (as GO terms) of genes up- and down-regulated during the first 30 min germination of one year-old conidia. Same legend as in Fig.3.

Figure 5

Different patterns of gene expression seen during the first 90 min of incubation of one-week old conidia in YPD medium. In bold is the main trend of the expression of the variation seen in the cluster.