The zinc cluster transcription factor Rha1 is a positive filamentation regulator in Candida albicans

Abstract

Zinc cluster transcription factors are essential fungal specific regulators of gene expression. In the dimorphic pathogen Candida albicans, they control processes ranging from metabolism and stress adaptation to mating, virulence, and antifungal resistance.Here, we have identified the gene CaORF19.1604 as encoding a zinc cluster transcription factor that acts as a regulator of filament development. Hyperactivation of CaORF19.1604, which we have named RHA1 for Regulator of Hyphal Activity, leads to a wrinkled colony morphology under non-hyphal growth conditions, to pseudohyphal growth and filament formation, to invasiveness and enhanced biofilm formation. Cells with activated Rha1 are sensitive to cell wall modifying agents such as Congo red and the echinocandin drug caspofungin but show normal sensitivity to fluconazole. RNAsequencing-based transcriptional profiling of the activated Rha1 strain reveals the upregulation of genes for core filamentation and cell-wall-adhesion-related proteins such as Als1, Als3, Ece1, and Hwp1. Upregulation is also seen for the genes for the hyphalinducing transcription factors Brg1 and Ume6 and genes encoding several enzymes involved in arginine metabolism, while downregulation is seen for the hyphal repressor Nrg1. The deletion of BRG1 blocks the filamentation caused by activated Rha1, while null mutants of UME6 result in a partial block. Deletion of RHA1 can partially reduce healthy hyphal development triggered by environmental conditions such as Spider medium or serum at 37°C.In contrast to the limited effect of either single mutant, the double rha1 ume6 deletion strain is totally defective in both serum and Spider medium stimulated hyphal development. While the loss of Brg1 function blocks serum-stimulated hyphal 4 development, this block can be significantly bypassed by Rha1 hyperactivity, and the combination of Rha1 hyperactivity and serum addition can generate significant polarization in even brg1 ume6 double mutants. Our results thus suggest that in response to external signals, Rha1 functions to facilitate the switch from an Nrg1 controlled yeast state to a Brg1/Ume6 regulated hyphal state. Author SummaryCandida albicans is the predominant human fungal pathogen, generating a mortality rate of 40% in systemically infected patients. The ability of Candida albicans to change its morphology is a determinant of its tissue penetration and invasion in response to variant host-related stimuli. The regulatory mechanism for filamentation includes a complex network of transcription factors that play roles in regulating hyphae associated genes.We identify here a new regulator of filamentation from the zinc cluster transcription factor family. We present evidence suggesting that this transcription factor assists the Nrg1/Brg1 switch regulating hyphal development.

Transcriptional Circuits Regulating Developmental Processes in Candida albicans

“…As such, several of the 50 auxiliary transcriptional regulators are integrated into the larger biofilm network that includes the core nine transcriptional regulators and all of their directly bound target genes (Nobile et al, 2012). Based on existing phenotypic analyses of the mutant strains of the auxiliary biofilm transcriptional regulators, the majority (48) are implicated in the regulation of adhesion and/or filamentation (Brown et al, 1999;Kadosh and Johnson, 2001;Cheng et al, 2003;Uhl et al, 2003;Garcıá-Sańchez et al, 2004;Kelly et al, 2004;Mulhern et al, 2006;Kim et al, 2008b;Shen et al, 2008;Wheeler et al, 2008;Homann et al, 2009;Nobile et al, 2009;Pukkila-Worley et al, 2009;Uppuluri et al, 2010a;Uppuluri et al, 2010b;Askew et al, 2011;Bonhomme et al, 2011;Ganguly et al, 2011;Finkel et al, 2012;Kamthan et al, 2012;Langford et al, 2013;Delgado-Silva et al, 2014;Tsai et al, 2014;Chen and Lan, 2015;Fox et al, 2015;Ghosh et al, 2015;Kakade et al, 2016;Kakade et al, 2019;Böttcher et al, 2020;Lagree et al, 2020;Omran et al, 2020;Wang et al, 2020); 16 are implicated in drug resistance and/or tolerance (Bruno et al, 2006;Cornet et al, 2006;Mulhern et al, 2006;Xu et al, 2007;…”

A Deep Learning Approach to Capture the Essence of Candida albicans Morphologies

“…Hyperactivation of Rha1 can trigger filamentous growth in the absence of external signals. In the presence of serum, it can bypass the need for Brg1 ( 62 ). Loss of Rha1 function leads to reduced ability to generate hyphal growth in the presence of external signatures.…”

A deep learning approach to capture the essence of Candida albicans morphologies

“…Regulator of Hyphal Activity 1 ( RHA1 ) encodes a zinc cluster transcription factor that serves as a regulator of the Nrg1/Brg1 switch. Hyperactivation of Rha1 can trigger filamentous growth in the absence of external signals or in the presence of serum can bypass the need for Brg1 62 . Loss of Rha1 function leads to reduced ability to generate hyphal growth in the presence of external signatures.…”