Low Dosage of Histone H4 Leads to Growth Defects and Morphological Changes in Candida albicans Lucia F. Zacchi1, Anna M. Selmecki2, Judith Berman1,2, Dana A. Davis1* 1 Department of Microbiology, University of Minnesota, Minneapolis, Minnesota, United States of America, 2 Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, Minnesota, United States of America Abstract Chromatin function depends on adequate histone stoichiometry. Alterations in histone dosage affect transcription and chromosome segregation, leading to growth defects and aneuploidies. In the fungal pathogen Candida albicans, aneuploidy formation is associated with antifungal resistance and pathogenesis. Histone modifying enzymes and chromatin remodeling proteins are also required for pathogenesis. However, little is known about the mechanisms that generate aneuploidies or about the epigenetic mechanisms that shape the response of C. albicans to the host environment. Here, we determined the impact of histone H4 deficit in the growth and colony morphology of C. albicans. We found that C. albicans requires at least two of the four alleles that code for histone H4 (HHF1 and HHF22) to grow normally. Strains with only one histone H4 allele show a severe growth defect and unstable colony morphology, and produce faster-growing, morphologically stable suppressors. Segmental or whole chromosomal trisomies that increased wild-type histone H4 copy number were the preferred mechanism of suppression. This is the first study of a core nucleosomal histone in C. albicans, and constitutes the prelude to future, more detailed research on the function of histone H4 in this important fungal pathogen. Citation: Zacchi LF, Selmecki AM, Berman J, Davis DA (2010) Low Dosage of Histone H4 Leads to Growth Defects and Morphological Changes in Candida albicans. PLoS ONE 5(5): e10629. doi:10.1371/journal.pone.0010629 Editor: Michael C. Lorenz, University of Texas-Houston Medical School, United States of America Received January 12, 2010; Accepted April 14, 2010; Published May 13, 2010 Copyright: 2010 Zacchi et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by the Investigators in Pathogenesis of Infectious Disease Award from the Burroughs Wellcome Fund to D.A.D., NIH R01 AI0624273 to J.B. and Microbial and Plant Genomics Institute of MN Integrative Fellowship to A.M.S. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: dadavis@umn.edu Introduction Candida albicans is a major human fungal pathogen and is the fourth most common cause of nosocomial bloodstream infections [1]. C. albicans is a common commensal of the skin and mucosa, and often causes superficial, non-life threatening infections at these sites [2]. However, in immune-compromised individuals C. albicans can cause systemic infections, which have a mortality rate of .30% even in patients undergoing antifungal therapy [3]. The steady increase in the population of immune-compromised individuals due to modern medical practices such as chemother- apy and organ transplantation, as well as because of the AIDS epidemic continues to provide niches for the development of C. albicans systemic and mucosal infections. C. albicans pathogenesis has been increasingly linked to alterations in chromosome structure and dynamics. C. albicans strains with altered karyotypes are frequently isolated from clinical samples, from passage through mammalian hosts, and by growth in specific carbon sources or antifungals in vitro [4,5]. C. albicans has a high tolerance to aneuploidies, perhaps because they provide a source for phenotypic variation, critical for survival and pathogenesis [6]. Aneuploidies are associated with antifungal resistance, metabolic changes, and mating [7–13]. Altered karyotypes have also been associated with variations in colony morphology [4,6,14,15]. However, the mechanisms that promote ploidy changes and genomic rearrangements are not well understood. Histone modifying enzymes and chromatin remodeling proteins also contribute to the regulation of pathogenesis traits. For example, mutants in histone deacetylases, methylases, acetyltrans- ferases, and members of chromatin remodeling complexes show defects in yeast-hyphal transitions, white-opaque switching, adhesion to epithelial cells, and/or antifungal and stress resistance [16–23]. Therefore, changes in the structure and function of the chromatin leads to epigenetic defects and potentially to karyotypic variations that have a direct impact on C. albicans virulence. Chromatin is a dynamic structure composed of DNA and DNA binding proteins that allows for an efficient storage and usage of the genetic information. The basic unit of chromatin architecture is the nucleosome, which is composed of the evolutionary conserved histones H2A, H2B, H3 and H4 assembled in a hetero-octamer of two H2A/H2B dimers and one H3/H4 tetramer. The DNA is wrapped around the nucleosome, constituting the first level of chromatin compaction. Due to this intimate relationship with the DNA, histones are involved in all processes associated with chromatin structure and function, including transcription, replication, DNA repair, recombination, and chromosome segregation. Histones participate in the regula- tion of these processes by providing a platform to transmit information to other proteins (e.g. DNA and RNA polymerases) through posttranslational modifications in their residues [24,25] and through nucleosomal occupancy of regulatory regions in the DNA [26,27]. Thus, histones constitute the primary regulators of chromatin activity. PLoS ONE | www.plosone.org 1 May 2010 | Volume 5 | Issue 5 | e10629