Yeast Yeast 2008; 25: 849–859. Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/yea.1636 Yeast Functional Analysis Report Role of Sho1p adaptor in the pseudohyphal development, drugs sensitivity, osmotolerance and oxidant stress adaptation in the opportunistic yeast Candida lusitaniae St´ ephanie Boisnard, Gwena¨ el Ruprich-Robert, Martine Florent, Bruno Da Silva, Florence Chapeland-Leclerc and Nicolas Papon* Programme Chimior´ esistance des Levures Pathog` enes, EA209 ‘Eucaryotes Pathog` enes: Transports Membranaires et Chimior´ esistance’, UFR des Sciences Pharmaceutiques et Biologiques, Universit´ e Paris Descartes, 75006 Paris, France *Correspondence to: Nicolas Papon, Programme Chimior´ esistance des Levures Pathog` enes, EA209 ‘Eucaryotes Pathog` enes: Transports Membranaires et Chimior´ esistance’, UFR des Sciences Pharmaceutiques et Biologiques, Universit´ e Paris Descartes, 4 Avenue de l’Observatoire, 75006 Paris, France. E-mail: nicolas.papon@univ- paris5.fr Received: 26 June 2008 Accepted: 17 September 2008 Abstract In 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 sho1  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 sho1  mutant does not display evident cell-wall architecture modifications, such as aggregation phenotypes. Although not hypersusceptible to antifungals of clinical relevance, the sho1  mutants are susceptible to the filamentous fungi-specific antifungals dicarboximides and phenylpyrroles. Finally, our findings highlight some significant phenotypic differences when the C. lusitaniae sho1  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. Keywords: morphogenesis; pseudohyphal development; oxidant stress; osmotoler- ance; drugs sensitivity; Candida lusitaniae Introduction In response to many stress conditions, unicellu- lar organisms undergo a severe modification of their gene-expression pattern. Repression of genes encoding proteins involved in growth-related pro- cesses lead to a temporary arrest in cell cycle progression, mRNA metabolism, protein synthe- sis and secretion pathways. On the other hand, cell survival requires a rapid induction of specific and protective genes in response to the environ- mental conditions. These stresses include changes in osmolarity, temperature, ionic and oxidative stresses. Copyright  2008 John Wiley & Sons, Ltd.