The transition between a unicellular yeast form to multicellular filaments is crucial for budding yeast foraging and the pathogenesis of many fungal pathogens such asCandida albicans. Here, we examine the role of the related transcription factors Ecm22 and Upc2 inSaccharomyces cerevisiaefilamentation. Overexpression of eitherECM22orUPC2leads to increased filamentation, whereas cells lacking bothECM22andUPC2do not exhibit filamentous growth. Ecm22 and Upc2 positively control the expression ofFHN1,NPR1,PRR2and sterol biosynthesis genes. These genes all play a positive role in filamentous growth, and their expression is upregulated during filamentation in an Ecm22/Upc2-dependent manner. Furthermore, ergosterol content increases during filamentous growth.UPC2expression also increases during filamentation and is inhibited by the transcription factors Sut1 and Sut2. The expression ofSUT1andSUT2in turn is under negative control of the transcription factor Ste12. We suggest that during filamentation Ste12 becomes activated and reducesSUT1/SUT2expression levels. This would result in increasedUPC2levels and as a consequence to transcriptional activation ofFHN1,NPR1,PRR2and sterol biosynthesis genes. Higher ergosterol levels in combination with the proteins Fhn1, Npr1 and Prr2 would then mediate the transition to filamentous growth.
The related budding yeast transcription factors Ecm22 and Upc2 are required for the transition of unicellular yeasts to multicellular filaments. They increase the expression ofPRR2,NPR1,FHN1and sterol biosynthesis genes during filamentation. These genes are either essential for filamentous growth or at least play an important role in this process. Upc2 itself is regulated at transcriptional level by the transcription factor Ste12.