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Mitochondrial two-component signaling systems in Candida albicans

ABSTRACT: Two-component signal transduction pathways are one of the primary means by which microorganisms respond to environmental signals. These signaling cascades originated in prokaryotes and were inherited by eukaryotes via endosymbiotic lateral gene transfer from ancestral cyanobacteria. We report here that the nuclear genome of pathogenic fungus Candida albicans contains elements of a two-component signaling pathway that seem to be targeted to the mitochondria. In C. albicans two-component response regulator protein Srr1(Stress Response Regulator) contains a mitochondrial targeting sequence at the N-terminus, and fluorescence microscopy reveals mitochondrial localization of GFP-tagged Srr1p. Moreover, phylogenetic analysis indicates that C. albicans Srr1p is more closely related to histidine kinases and response regulators found in marine bacteria compared to other two-component proteins present in the fungi. These data suggest conservation of this protein during the evolutionary transition from endosymbiont to a subcellular organelle. We used microarray analysis to determine if the phenotypes observed with srr1Δ/Δ mutant could be correlated with gene transcriptional changes. Expression of mitochondrial genes was altered in the srr1Δ/Δ null mutant in comparison to the wild type. Furthermore, apoptosis significantly increased in the srr1Δ/Δ mutant strain compared to wild type, suggesting activation of mitochondria dependent apoptotic cell death pathway in the srr1Δ/Δ mutant. This study shows for the first time that a lower eukaryote like C. albicans possesses a two-component response regulator protein that has survived in mitochondria and regulates a subset of genes whose functions are associated with oxidative stress response and programmed cell death (apoptosis).

ORGANISM(S): Candida albicans

PROVIDER: GSE45438 | GEO | 2013/07/02

SECONDARY ACCESSION(S): PRJNA194389

REPOSITORIES: GEO

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Project description:Mitochondria generate signals of adaptation that regulate nuclear genes expression via retrograde signaling. But this phenomenon is complexified when qualitatively different mitochondria and mitochondrial DNA (mtDNA) coexist within cells. Although this cellular state of heteroplasmy leads to divergent phenotypes clinically, its consequences on cellular function and the cellular transcriptome are unknown. To interrogate this phenomenon, we generated somatic cell cybrids harboring increasing levels of a common mtDNA mutation (tRNALeu(UUR) 3243A>G) and mapped the resulting cellular phenotypes and transcriptional profiles across the complete range of heteroplasmy. Small increases in mutant mtDNAs caused relatively modest defect in mitochondrial oxidative capacity, but resulted in sharp transitions in mitochondrial ultrastructure and in the nuclear and mitochondrial transcriptomes, with the critical functional threshold corresponding to the induction of epigenetic regulatory systems. Principal component analysis underscores how each heteroplasmy level occupies a different "transcriptional space", with low levels heteroplasmy (20-30%) producing a dose-response linear progression in one direction, and mutationload of 50, 60 and 90% producing changes in the opposite direction. Hence, subtle changes in mitochondrial energetics can act through the epigenome to generate the phenotypes of the common “complex” diseases. Cells were generated by transferring the wildtype (3243A) and mutant (3243G) mtDNAs from a heteroplasmic 3243A>G patient’s lymphoblastoid cell line into 143B(TK-) mtDNA-deficient (ρo) cells and selected for transmitochondrial cybrids. Subsequent mtDNA depletion, reamplification, and cloning (Wiseman and Attardi, 1978) resulted in a series of stable cybrids harboring approximately 0, 20, 30, 50, 60, 90, and 100% 3243G mutant mtDNAs. Total RNA extracted from each cell line was then extracted, depleted of rRNA, and measured in sequenced in triplicates.

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Mitochondrial two-component signaling systems in Candida albicans

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