The role of the sakA (Hog1) and tcsB (s1n1) genes in the oxidant adaptation of Aspergillus fumigatus

The Hog1 MAP kinase pathway regulates stress adaptation in several fungi. To assess its role in stress adaptation in Aspergillus fumigatus, we constructed mutants in genes encoding the sensor histidine kinase (HK) tcsB as well as sakA, which are homologues of the Saccharomyces cerevisiae sln1 and Hog1, respectively. Compared to the wild type strain (Wt), growth of sakA (sakAD) mutant was reduced, and growth inhibition was increased when H2O2, menadione, or SDS was added to the media. On the other hand, the tcsB mutant (tcsB Delta) was similar to the Wt strain in regard to growth and morphology, although a partial sensitivity to SDS was observed. Western blot analysis of Wt and the tcsBD strains indicated that when stressed with H2O2, phosphorylation of Hog1p still occurs in the mutant. Since in Candida albicans, Hog1 regulates transcription of at least one histidine kinase, we performed RT-PCR of 6 histidine kinase genes as well as the ssk1 and skn7 response regulator genes of A. fumigatus. No significant differences in transcription were observed with the sakA Delta when compared to the Wt, indicating that the sakA does not regulate transcription of these genes. Our studies indicate that the A. fumigatus sakA is required for optimal growth of the organism with or without oxidant stress, while tcsB gene is dispensable.