Reinforcement amid genetic diversity in the Candida albicans biofilm regulatory network

Abstract

Biofilms of the fungal pathogen Candida albicans include abundant long filaments called hyphae. These cells express hypha-associated genes, which specify diverse virulence functions including surface adhesins that ensure biofilm integrity. Biofilm formation, virulence, and hypha-associated gene expression all depend upon the transcription factor Efg1. This transcription factor has been characterized extensively in the C. albicans type strain SC5314 and derivatives, but only recently has its function been explored in other clinical isolates. Here we define a principal set of Efg1-responsive genes whose expression is significantly altered by an efg1Δ/Δ mutation across 17 clinical isolates. This principal gene set includes 68 direct Efg1 targets, whose 5’ regions are bound by Efg1 in five clinical isolates, and 42 indirect Efg1 targets, whose 5’ regions are not detectably bound by Efg1. Three direct Efg1 target genes encode transcription factors—BRG1, UME6, and WOR3 –whose increased expression in an efg1Δ/Δ mutant restores expression of multiple indirect and direct principal targets, as well as biofilm formation ability. Although BRG1 and UME6 are well known positive regulators of hypha-associated genes and biofilm formation, WOR3 is best known as an antagonist of Efg1 in the sexual mating pathway. We confirm the positive role of WOR3 in biofilm formation with the finding that a wor3Δ/Δ mutation impairs biofilm formation in vitro and in an in vivo biofilm model. Positive control of Efg1 direct target genes by other Efg1 direct target genes–BRG1, UME6, and WOR3 –may buffer principal Efg1-responsive gene expression against the impact of genetic variation in the C. albicans species.

Alternative sulphur metabolism in the fungal pathogen Candida parapsilosis

“…Several recent studies have shown that gene disruptions can result in different phenotypes in different isolates of the same species [39][40][41] . Because our observation that C. parapsilosis Met4 is not the sole regulator of sulphur amino acid biosynthesis is surprising, we tested the effect of disrupting both MET4 and MET28 in different genetic backgrounds and in isolates from different C. parapsilosis clades 42 .…”

Functional Dichotomy for a Hyphal Repressor in Candida albicans

“…We focused specifically on hypha-associated genes to determine whether the nrg1 Δ/Δ mutation affected these genes differently in the two strain backgrounds. We used a set of 152 genes derived from comparisons of strongly and weakly filamentous C. albicans strains ( 23 ). The P57055 nrg1 Δ/Δ mutant had downregulated RNA levels for 17 of the genes ( Fig.…”

“…RNA-Seq, read mapping, and differential expression analysis using the DESeq2 R package (1.14.1) were performed by Novogene (Sacramento, CA), using three biological replicates per group ( Text S1 ). (A) Heat map representation of expression differences in 152 hypha-associated genes ( 23 ). Comparisons include P57055 nrg1 Δ/Δ versus P57055 WT (comparison 1), SC5314 nrg1 Δ/Δ versus SC5314 WT (comparison 2), P57055 WT versus SC5314 WT (comparison 3), and P57055 nrg1 Δ/Δ versus SC5314 nrg1 Δ/Δ (comparison 4).…”

Biofilm-associated metabolism via ERG251 in Candida albicans

“…Efg1 is required for biofilm formation in multiple C . albicans clinical isolates [ 30 , 31 ], a feature that distinguishes it from other biofilm master regulators [ 30 ]. Efg1 controls expression of ~800 genes in any one strain [ 30 , 31 ], a lot to study effectively.…”

“…Efg1 controls expression of ~800 genes in any one strain [ 30 , 31 ], a lot to study effectively. However, there is limited overlap among Efg1-regulated genes among clinical isolates [ 30 , 31 ], due in part to differences in expression of partner proteins that shape Efg1 outputs [ 32 ]. Only 110 genes are under Efg1 control in all 17 isolates we examined [ 31 ], a more manageable number of genes for functional analysis.…”