## 5 Role of the Osmotic Stress-response Pathway on Fungal Development and Secondary Metabolism  
The study of the HOG pathway and its implications in morphological development and secondary metabolism in filamentous fungi are still at the earliest stages. In _A. nidulans_, a _sakA_ deletion mutant shows development and cell-specific phenotypes [46]. This mutant is characterized by premature sexual development. In addition, deletion of _sakA_ results in conidia that are highly sensitive to oxidative and heat shock stress and lose viability overtime. This evidence supports the role of SakA as a repressor of sexual development and asexual spore stress resistance and survival. As mentioned in section 3, another member of the _A. nidulans_ HOG pathway, SskA is important in regulating the tolerance of conidia to osmotic stress. SakA was also shown to be involved in conidia viability in _A. fumigatus_, where the _sakA_ mutant presented alterations in conidia germination in a nitrogen source-dependent manner [68]. The bZip-type transcription factor AtfA (putative ortholog of _S. pombe_ Atf1), that functions downstream of the HogA MAPK in the course of fluidoxonil and osmotic stress response, is also involved in conidia stress tolerance [58, 59, 69, 70]. Also in _A. fumigatus_, mutations in MA21, a homolog of the _S. cerevisiae_ transmembrane sensor kinase _SHO_ gene, showed a reduction in growth and germination rates. It demonstrated irregular hyphal morphology with a decrease in phialides and conidia [71]. Development is also affected by osmoregulation in dimorphic fungi such as _Candida albicans_, where the HOG homolog is necessary for chlamdospore formation [72]. Additionally, studies on _A. nidulans_ SteC revealed its role in morphogenesis. Deletion of the _steC_ gene results in a slower growth rate, increase of branched hyphae, alteration of conidiophore morphology, inhibition of heterokaryon formation and a blockage of cleistothecial development. The gene is transcriptionally activated during asexual development and controls the phosphorylation of two putative MAP kinases [57]. Also, RocA (homolog of _S. cerevisiae_ Tup1p) affects growth and sexual/asexual development in _A. nidulans_[73, 74]. The response regulators SrrA and SskA are not only involved in osmotic and oxidative stress signal transduction but also in regulation of asexual development in _A. nidulans_. Deletion of any one of these genes results in a reduction in conidiation and spore viability [48]. The evidence provided by _A. nidulans_ studies as well as studies in other fungi clearly indicates a connection between the osmotic stress regulatory system and fungal development. Recently in our laboratories we found that osmotic stress caused by high concentrations of sodium chloride, sorbitol or potassium chloride positively affects vegetative growth leads to an increase in conidiation in _A. flavus_ ([PERSON] _et al._, manuscript in preparation). [PERSON] _et al._[75] also reported an increase of conidiation in the presence of high amount of sorbitol in _A. nidulans_. In contrast, in a study by [PERSON] and [PERSON] [76] where _A. flavus_ was inoculated on NaCl medium, a reduction of conidia was observed. The _A. flavus_ strains are genetically diverse and they have been sub-divided into two strain types, S and L, based differences in sclerotial size [77]. It is possible that this variability in conidiation could be the result of different _A. flavus_ strains used in these studies leading to different responses to osmotic stress and salinity. It is also possible that other culture conditions could have caused the observed differences in conidiation under induced osmotic stress. In addition, our recent study showed the light-dependent global regulator VeA, known to control sexual/asexual morphogenesis and secondary metabolism in filamentous fungi [78], to be associated with the osmotic-stress response in _A. flavus_ ([PERSON] _et al._, manuscript in preparation and Figure 1). Specifically, osmostress enhances hyperconidiation in the _A.