Identification of <i>SFL1</i> as a positive regulator for flor formation in <i>Zygosaccharomyces rouxii</i>

Some wild <i>Zygosaccharomyces rouxii</i> impair the quality of soy sauce through the generation of unpleasant odors induced by the formation of flor. Flor formation in <i>Z. rouxii</i> depends on the expression of the <i>FLO11D</i> gene, which is a homolog of the <i>FLO11</i> gene that encodes a cell surface protein in <i>Saccharomyces cerevisiae. FLO11</i> expression in <i>S. cerevisiae</i> is regulated by multiple pathways. To investigate the regulation of <i>FLO11D</i> expression in <i>Z. rouxii</i>, we created 13 gene knockout mutants (<i>STE12, TEC1, HOG1, MSS11, FLO8, MSN1, MSN2/4, SKO1, TUP1, CYC8, YAK1, MIG1</i>, and <i>SFL1</i>) related to those pathways and examined whether these mutants form flor. Unexpectedly, <i>SFL1</i> knockout mutant could only form a very weak flor due to decreased <i>FLO11D</i> expression, suggesting that <i>SFL1</i> acts as a potential activator of flor formation through <i>FLO11D</i> expression. This result is in contrast to <i>S. cerevisiae SFL1</i>, which acts as a repressor of <i>FLO11</i> expression. In <i>Zygoassacharomyces rouxii, SFL1</i> acts as a potential activator of flor formation through <i>FLO11D</i> expression although <i>SFL1</i> is a repressor of <i>FLO11</i> in <i>Saccharomyces cerevisiae.</i>