Abstract
BackgroundFungal conidia are usually dormant unless the extracellular conditions are right for germination. Despite the importance of dormancy, little is known about the molecular mechanism underlying entry to, maintenance of, and exit from dormancy. To gain comprehensive and inter-species insights, transcriptome analyses were conducted across Aspergillus fumigatus, Aspergillus niger, and Aspergillus oryzae.ResultsWe found transcripts of 687, 694, and 812 genes were enriched in the resting conidia compared with hyphae in A. fumigatus, A. niger, and A. oryzae, respectively (conidia-associated genes). Similarly, transcripts of 766, 1,241, and 749 genes were increased in the 1 h-cultured conidia compared with the resting conidia (germination-associated genes). Among the three Aspergillus species, we identified orthologous 6,172 genes, 91 and 391 of which are common conidia- and germination-associated genes, respectively. A variety of stress-related genes, including the catalase genes, were found in the common conidia-associated gene set, and ribosome-related genes were significantly enriched among the germination-associated genes. Among the germination-associated genes, we found that calA-family genes encoding a thaumatin-like protein were extraordinary expressed in early germination stage in all Aspergillus species tested here. In A. fumigatus 63 % of the common conidia-associated genes were expressed in a bZIP-type transcriptional regulator AtfA-dependent manner, indicating that AtfA plays a pivotal role in the maintenance of resting conidial physiology. Unexpectedly, the precocious expression of the germination-associated calA and an abnormal metabolic activity were detected in the resting conidia of the atfA mutant, suggesting that AtfA was involved in the retention of conidial dormancy.ConclusionsA comparison among transcriptomes of hyphae, resting conidia, and 1 h-grown conidia in the three Aspergillus species revealed likely common factors involved in conidial dormancy. AtfA positively regulates conidial stress-related genes and negatively mediates the gene expressions related to germination, suggesting a major role for AtfA in Aspergillus conidial dormancy.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2689-z) contains supplementary material, which is available to authorized users.
Highlights
Fungal conidia are usually dormant unless the extracellular conditions are right for germination
Transcriptome determination using RNA-sequencing To compare the conidial transcriptomes of different Aspergillus species, the conidia of each strain should be harvested from physiologically similar cultivation conditions
Based on the colony expansion rates, conidia production rates, and germination rates (Additional file 1), we grew them at preferred temperature condition, namely A. fumigatus were grown at 37 °C, A. niger at 30 °C, and A. oryzae at 30 °C on potato dextrose agar (PDA)
Summary
Fungal conidia are usually dormant unless the extracellular conditions are right for germination. Despite the importance of dormancy, little is known about the molecular mechanism underlying entry to, maintenance of, and exit from dormancy. In general, stress-tolerant reproductive structures, and filamentous fungi vigorously produce conidia under the appropriate conditions [1]. In the presence of water and appropriate nutrients, conidia germinate, whereas conidia enter dormancy when the environment is not appropriate. Dormant conidia do not consume energy prior to encountering the appropriate conditions for germination. This mechanism allows conidia to find an environment where the fungi can prosper, which contributes to their ubiquity and prosperity in nature. Despite its significance to conidial physiology, the molecular mechanisms underlying entering and exiting dormancy remain largely unknown
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