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Eukaryotic Cell, October 2007, p. 1736-1744, Vol. 6, No. 10
1535-9778/07/$08.00+0 doi:10.1128/EC.00236-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Carlsberg Laboratory, Yeast Biology, Gamle Carlsberg Vej 10, DK-2500 Valby, Copenhagen, Denmark; Department of Microbiology, Friedrich-Schiller-University, Jena, Germany; and Junior Research Group, Fungal Pathogens, Leibniz Institute for Natural Product Research and Infection Biology—Hans-Knöll Institute, Jena, Beutenbergstr., 11a, D-07745 Jena, Germany
Received 29 June 2007/ Accepted 17 August 2007
Hyphal morphogenesis in Candida albicans is regulated by multiple pathways which act by either inducing or repressing filamentation. Most notably, Tup1, Nrg1, and Rfg1 are transcriptional repressors, while Efg1, Flo8, Cph1, and Czf1 can induce filamentation. Here, we present the functional analysis of CaSFL1, which encodes the C. albicans homolog of the Saccharomyces cerevisiae SFL1 (suppressor of flocculation) gene. Deletion of CaSFL1 results in flocculation (i.e., the formation of clumps) of yeast cells, which is most pronounced in minimal medium. The flocs contained hyphae already under noninducing conditions, and filamentation could be enhanced with hypha-inducing cues at 37°C. Expression of SFL1 in a heterozygous mutant under the control of the CaMET3 promoter was shown to complement these defects and allowed switching between wild-type and mutant phenotypes. Interestingly, increased expression of SFL1 using a MET3prom-SFL1 construct prior to the induction of filamentation completely blocked germ tube formation. To localize Sfl1 in vivo, we generated a SFL1-GFP fusion. Sfl1-green fluorescent protein was found in the nucleus in both yeast cells and, to a lesser extent, hyphal cells. Using reverse transcription-PCR, we find an increased expression of ALS1, ALS3, HWP1, ECE1, and also FLO8. Our results suggest that Sfl1 functions in the repression of flocculation and filamentation and thus represents a novel negative regulator of C. albicans morphogenesis.
Published ahead of print on 31 August 2007.
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