NRG1, a repressor of filamentous growth in C.albicans, is down-regulated during filament induction

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Abstract
In response to a variety of external signals, the fungal pathogen Candida albicans undergoes a transition between ellipsoidal single cells (blastospores) and filaments composed of elongated cells attached end‐to‐end. Here we identify a DNA‐binding protein, Nrg1, that represses filamentous growth in Candida probably by acting through the co‐repressor Tup1. nrg1 mutant cells are predominantly filamentous under non‐filament‐inducing conditions and their colony morphology resembles that of tup1 mutants. We also identify two filament‐specific genes, ECE1 and HWP1 , whose transcription is repressed by Nrg1 under non‐inducing conditions. These genes constitute a subset of those under Tup1 control, providing further evidence that Nrg1 acts by recruiting Tup1 to target genes. We show that growth in serum at 37°C, a potent inducer of filamentous growth, causes a reduction of NRG1 mRNA, suggesting that filamentous growth is induced by the down‐regulation of NRG1 . Consistent with this idea, expression of NRG1 from a non‐regulated promoter partially blocks the induction of filamentous growth.