Taken together with findings in this study, it appears that a robust and complex signal transduction system for adaptation to extracellular environments exists in A. fumigatus. In conclusion, we found that NikA plays an important role in conidiation, morphology, and stress responses, and that the SakA MAPK cascade is regulated through SskA in response to osmotic shock and fungicide treatment. We also characterized the other HKs including Fos1, PhkA, PhkB, Fhk5, and Fhk6. There were no interactions between these HKs and NikA or SakA, at least under the conditions tested here. Although NikA seems to be dispensable in A. fumigatus pathogenicity, molecular insights provided in this study may open possibilities in the NVP-BKM120 944396-07-0 development of new antifungal chemicals focusing on the TCS signaling of medically relevant fungal pathogens. Bacterial pathogens subvert host eukaryotic cellular pathways for survival and replication; in turn, infected host cells respond to the invading pathogen through cascading changes in gene expression. Deciphering these complex temporal and spatial dynamics to identify novel bacterial virulence factors or host response pathways is crucial for improved diagnostics and therapeutics. Microarrays have been the predominant methodology for determining gene expression profiles, revealing a diversity of bacterial pathogenic mechanisms and commonalities of the complex global host response to infection. However, microarrays are inadequate for profiling both prokaryotic and eukaryotic RNA from infected cells, as they are limited to what can be printed and detected on the array. Technical limitations such as high background signals and cross-hybridization also limits their dynamic range. Consequently, array analyses of hostpathogen interactions have typically examined either the pathogen or the host, but usually not both simultaneously. The few studies that examine both bacterial and host cell transcriptional responses separate the prokaryotic and eukaryotic messenger RNA prior to microarray profiling. Sufficient prokaryotic mRNA for hybridization can be difficult to obtain unless axenic culture or selective amplification is used or, in the case of intracellular bacteria, in vitro infections are established with high multiplicities of infection. High MOIs may not represent natural infection levels, distorting expression profiles. The early events following invasion are often poorly characterized, as the small number of organisms yields insufficient transcripts for microarray detection. Furthermore, standard microarrays are restricted to ALK5 Inhibitor II citations existing genome annotation and cannot detect novel RNA moieties that are not printed on the array. Tiling arrays overcome this limitation and have been successfully applied to bacteria, revealing antisense RNA expression and other non-coding RNA transcripts. However, the large size of eukaryotic genomes makes tiling arrays prohibitively expensive for host gene expression studies. Tag-based sequencing methods alleviate these problems to some extent, allowing individual transcripts to be digitally counted with a broad dynamic range. Nevertheless, as these approaches only sample a small region of a transcript, they cannot capture the full diversity of RNA classes and isoforms. RNA-Seq, or deep sequencing of cDNA libraries by nextgeneration sequencing, circumvents many of the problems associated with microarray profiling or tag-based sequencing. RNA-Seq can comprehensively and systematically define the transcriptome of an organism with minimal bias, across different experimental conditions or cell types without 
probe design or cross-hybridization problems. RNA-Seq data are consistent with microarray results but are more sensitive, with essentially an infinite dynamic range. RNA-Seq is annotationindependent, allowing novel transcript discovery without being reliant on array design or preexisting annotation.