Obligate sexual reproduction of a homothallic fungus closely related to the <i>Cryptococcus</i> pathogenic species complex.

Abstract

eLife digest.Fungi are enigmatic organisms that flourish in soil, on decaying plants, or during infection of animals or plants. Growing in myriad forms, from single-celled yeast to multicellular molds and mushrooms, fungi have also evolved a variety of strategies to reproduce. Normally, fungi reproduce in one of two ways: either they reproduce asexually, with one individual producing a new individual identical to itself, or they reproduce sexually, with two individuals of different 'mating types' contributing to produce a new individual. However, individuals of some species exhibit 'homothallism' or self-fertility: these individuals can produce reproductive cells that are universally compatible, and therefore can reproduce sexually with themselves or with any other cell in the population.Homothallism has evolved multiple times throughout the fungal kingdom, suggesting it confers advantage when population numbers are low or mates are hard to find. Yet some homothallic fungi been overlooked compared to heterothallic species, whose mating types have been well characterised. Understanding the genetic basis of homothallism and how it evolved in different species can provide insights into pathogenic species that cause fungal disease.With that in mind, Passer, Clancey et al. explored the genetic basis of homothallism in Cryptococcus depauperatus, a close relative of C. neoformans, a species that causes fungal infections in humans. A combination of genetic sequencing techniques and experiments were applied to analyse, compare, and manipulate C. depauperatus' genome to see how this species evolved self-fertility.Passer, Clancey et al. showed that C. depauperatus evolved the ability to reproduce sexually by itself via a unique evolutionary pathway. The result is a form of homothallism never reported in fungi before. C. depauperatus lost some of the genes that control mating in other species of fungi, and acquired genes from the opposing mating types of a heterothallic ancestor to become self-fertile.Passer, Clancey et al. also found that, unlike other Cryptococcus species that switch between asexual and sexual reproduction, C. depauperatus grows only as long, branching filaments called hyphae, a sexual form. The species reproduces sexually with itself throughout its life cycle and is unable to produce a yeast (asexual) form, in contrast to other closely related species.This work offers new insights into how different modes of sexual reproduction have evolved in fungi. It also provides another interesting case of how genome plasticity and evolutionary pressures can produce similar outcomes, homothallism, via different evolutionary paths. Lastly, assembling the complete genome of C. depauperatus will foster comparative studies between pathogenic and non-pathogenic Cryptococcus species.

Department

Description

Provenance

Subjects

Humans, Saccharomyces cerevisiae, Cryptococcus neoformans, Reproduction, Genes, Mating Type, Fungal, Biological Evolution

Citation

Published Version (Please cite this version)

10.7554/elife.79114

Publication Info

Passer, Andrew Ryan, Shelly Applen Clancey, Terrance Shea, Márcia David-Palma, Anna Floyd Averette, Teun Boekhout, Betina M Porcel, Minou Nowrousian, et al. (2022). Obligate sexual reproduction of a homothallic fungus closely related to the Cryptococcus pathogenic species complex. eLife, 11. p. e79114. 10.7554/elife.79114 Retrieved from https://hdl.handle.net/10161/33024.

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Scholars@Duke

Sun

Sheng Sun

Associate Research Professor in Molecular Genetics and Microbiology
Heitman

Joseph Heitman

Chair, Department of Molecular Genetics and Microbiology

Joseph Heitman was an undergraduate at the University of Chicago (1980-1984), graduating from the BS-MS program with dual degrees in chemistry and biochemistry with general and special honors. He then matriculated as an MD-PhD student at Cornell and Rockefeller Universities and worked with Peter Model and Norton Zinder on how restriction enzymes recognize specific DNA sequences and how bacteria respond to and repair DNA breaks and nicks. Dr. Heitman moved as an EMBO long-term fellow to the Biocenter in Basel Switzerland where, in studies with Mike Hall and Rao Movva, pioneered the use of yeast as a model for studies of immunosuppressive drug action. Their studies elucidated the central role of FKBP12 in forming complexes with FK506 and rapamycin that inhibit cell signaling and growth, discovered Tor1 and Tor2 as the targets of rapamycin, and contributed to the appreciation that immunosuppressive drugs inhibit signal transduction cascades that are conserved from yeasts to humans.

Dr. Heitman moved to Duke University in 1992, and is a member of the Department of Molecular Genetics and Microbiology where his studies focus on microorganisms addressing fundamental biological questions and unmet medical needs.  Dr. Heitman and colleagues focus on model and pathogenic yeasts including Cryptococcus neoformans and other diverse species from the fungal kingdom. Their studies with fungi as genetic models have revealed biological and genetic principles that can be generalized as models for eukaryotic cell and organism function. These include discovering FKBP12 and Tor1/2 as the targets of the immunosuppressive anti-proliferative natural product rapamycin, elucidating central roles of the calcium activated phosphatase calcineurin governing fungal virulence and morphogenesis and antifungal drug action, deciphering how cells sense and respond to nutrients via permeases, G protein coupled receptors, and the Tor signaling cascade, and illustrating how both model and pathogenic fungi sense both the environment and the infected host. In parallel, their studies address the evolution, structure, and function of fungal mating type loci as models for gene cluster and sex chromosome evolution.  The discovery of an ancestral sex determining locus in the basal fungal lineages involving two HMG domain proteins, SexM and SexP, homologous to the mammalian Sry sex determinant provides insights into both the origins of sex specification and its plasticity throughout the radiation of the fungal and metazoan kingdoms from their last shared common ancestor.  Their discovery of unisexual mating in fungi and subsequent analysis of its impact on the evolution of eukaryotic microbial pathogens provides insights into both microbial evolution and pathogenesis and how sexual reproduction may have first evolved.  Recent studies have unveiled novel mechanisms of antimicrobial drug resistance involving epimutations that silence drug-target genes via RNAi, functions of RNAi in genomic integrity of microbial pathogens, and loss of RNAi in hypervirulent outbreak lineages.

Dr. Heitman is a recipient of the Burroughs Wellcome Scholar Award in Molecular Pathogenic Mycology (1998-2005), the 2002 ASBMB AMGEN award for significant contributions using molecular biology to our understanding of human disease, and the 2003 Squibb Award from the Infectious Diseases Society of America (IDSA) for outstanding contributions to infectious disease research, the 2018 Korsmeyer Award from the American Society for Clinical Investigation, and the 2018 Rhoda Benham Award from the Medical Mycological Society of the Americas.  He is the recipient of an NIH/NIAID MERIT award 2011-2021 in support of studies on fungal unisexual reproduction in microbial pathogen evolution, a Duke University translational research mentoring award in 2012, and a Dean’s Award for Excellence in Mentoring from the Duke Graduate School in 2018.  He has served as an instructor in residence since 1998 for the Molecular Mycology Course at the Marine Biological Laboratory at Woods Hole, MA. Dr. Heitman is an editor for the journals PLOS GeneticsGenetics (2012-2017)PLOS Pathogens (Pearls review editor), Current Genetics (2001-2014)mBio, and Fungal Genetics and Biology; a member of the editorial boards of PLOS BiologyCurrent BiologyCell Host and Microbe, and PeerJ; former editor for PLOS Pathogens (mycology section editor, 2008-2011) and Eukaryotic Cell (2002-2012); an advisory board member for the Fungal Genome Initiative at the Broad Institute, the Fungal Kingdom Genome Project at the Department of Energy Joint Genome Institute, the NIAID Genomic Sequencing Centers for Infectious Diseases, and for the Integrated Microbial Biodiversity Program at the Canadian Institute for Advanced Research (CIFAR); co-chair for the Duke Chancellor’s Science Advisory Council (2009-2010); and co-chair/chair for the FASEB summer conference on Microbial Pathogenesis: Mechanisms of Infectious Disease (2011, 2013).  He was elected a member of the American Society for Clinical Investigation (ASCI) in 2003, a fellow of the Infectious Diseases Society of America (IDSA) in 2003, a fellow of the American Academy of Microbiology in 2004, a fellow of the American Association for the Advancement of Science (AAAS) in 2004, a member of the Association of American Physicians (AAP) in 2006, and a member of the American Academy of Arts & Sciences in 2020.  Dr. Heitman was an investigator with the Howard Hughes Medical Institute from 1992 to 2005. Dr. Heitman served as the director for the Duke University Program in Genetics and Genomics (UPGG) from 2002-2009 (including writing two funded competitive renewals for the T32 NIH training grant and establishing the annual program retreat). He was the founding director for the Center for Microbial Pathogenesis (now called the Center for Host-Microbial Interactions, CHoMI) and served in this capacity January 2002-October 2014.  He is currently the director of the Tri-institutional (Duke, UNC-CH, NC State) Molecular Mycology and Pathogenesis Training Program (MMPTP) (since July 1, 2012), and Chair of the Department of Molecular Genetics and Microbiology (since September 1, 2009).


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