Transcriptional profiling for Aspergillusnidulans HogA MAPK signaling pathway in response to fludioxonil and osmotic stress

Abstract

In filamentous fungi, the His–Asp phosphorelay signaling system and HOG pathway are involved in the action of the fungicides, fludioxonil, and iprodione, as well as osmotic and oxidative stress responses. Aspergillus nidulans response regulators (RRs), SskA and SrrA, and histidine kinase (HK), NikA, are involved in the growth inhibitory effects of these fungicides. To gain further insights into the molecular basis for these signaling systems, we performed DNA microarray analyses of fludioxonil and osmotic stress responses in A. nidulans. A global expression analysis revealed that a large number of genes were modulated by fludioxonil treatment in an SskA-dependent manner, whereas SrrA hardly contributed to this modulation. The fludioxonil up-regulated or down-regulated genes (FUGs or FDGs, respectively) are also dependent on the HogA MAPK cascade. We found that the SskA–HogA pathway regulates expression of atfA gene encoding a transcription factor involved in conidia stress tolerance. From the results of microarray analyses, AtfA-dependent FUGs largely overlapped with HogA-dependent FUGs, suggesting that AtfA functions downstream of the HogA MAPK. A series of microarray analyses showed that the inferred SskA–HogA–AtfA pathway is implicated in the transcriptional response to osmotic stress as well as fludioxonil. The srrA atfA null double mutant turns off the SrrA and SskA–HogA–AtfA pathways and showed sensitivity to osmotic stress but no resistance to fludioxonil. Our data revealed that the growth inhibitory effect of fludioxonil depends on factors other than AtfA in spite of the fact that AtfA functions downstream of the HogA MAPK cascade. The complexity of the stress response in the His–Asp phosphorelay system followed by the HogA MAPK cascade is discussed.