AbstractIn yeast, external signals such as high osmolarity or oxidant conditions activate the high osmolarity glycerol (HOG) mitogen‐activated protein kinase (MAPK) cascade pathway, which consists of two upstream branches, i.e. Sho1p and Sln1p and common downstream elements, including the Pbs2p MAPK kinase and the Hog1p MAPK. We recently showed that the Candida lusitaniae SLN1 gene, potentially encoding a histidine kinase receptor, is crucial for oxidative stress adaptation when the fungus grows as budding yeast and during the early steps of pseudohyphal development. In the current study, we characterized the SHO1 gene of this opportunistic fungus. Complete loss of SHO1 function causes profound defects in pseudohyphal differentiation, especially in high osmolarity and oxidative stress conditions, suggesting a crucial role of SHO1 in the pseudohyphae morphogenetic transitions. Moreover, when grown as budding yeast, the sho1Δ mutant revealed a sensitivity to compounds that interfere with the cell wall assembly, pointing to a potential role of Sho1p in cell wall biogenesis. However, the sho1Δ mutant does not display evident cell‐wall architecture modifications, such as aggregation phenotypes. Although not hypersusceptible to antifungals of clinical relevance, the sho1Δ mutants are susceptible to the filamentous fungi‐specific antifungals dicarboximides and phenylpyrroles. Finally, our findings highlight some significant phenotypic differences when the C. lusitaniae sho1Δ mutant is compared with the corresponding mutants described in Saccharomyces cerevisiae, Candida albicans and Aspergillus fumigatus. The GeneBank Accession No. for C. lusitaniae SHO1 gene is EU797514. Copyright © 2008 John Wiley & Sons, Ltd.