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Slice of PLOS: A Fungus Among Us

Fungi are essential elements of all ecosystems and provide many important services, most notably decomposition. While the classic role of fungi is in breaking down organic matter, fungi are incredibly varied and diverse, with members ranging from hyper-virulent pathogens to essential symbiotic partners of many plants. To highlight and promote the amazing contribution of fungi to our world, The British Mycological Society has created UK Fungus Day, occurring this year on October 9, 2016. As our contribution to the event, we here present some of the newest research from the Open Access corpus featuring fungi.

 

Fungal pathogens can infect a wide range of hosts. In recent years, Chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis, has devastated amphibian populations in Costa Rica and Panamá. In this PLOS ONE article, the authors document the spread of the fungus in frogs found in the lowland habitats east of the Panamá Canal [1]. Another PLOS ONE article found that 19.5% of amphibians tested positive for the fungus in a central African biodiversity hotspot, the Albertine Rift [2].

Image credit: U.S. Department of Agriculture
Amphibians are threatened by fungal disease. Image credit: U.S. Department of Agriculture

A fungus is also responsible for Panama Disease, which essentially wiped out an entire cultivar of bananas in the 1950s. Unfortunately, new strains of the fungus responsible for Panama Disease, Fusarium oxysporum f.sp. cubense, have evolved and threaten the current most popular banana cultivar, Cavendish. Interestingly, both the banana host and the fungal pathogens are clonal populations, as described in this PLOS Pathogens article [3]. Sigatoka Disease, caused by fungi of the genus Pseudocercospora, also threatens bananas. Using a comparative genomic analysis of the three fungal species responsible for Sigatoka Disease, this PLOS Genetics papers investigates the evolution of virulence-associated genes [4]. By sequencing P. fijiensis, the authors of this PLOS Genetics article document fungicide resistance markers and identify a potential assay for identifying resistant banana cultivars [5]. See this PLOS Biologue post for more about banana diseases.

Image credit: 10.1371/journal.pgen.1005904
Banana leaves infected with Sigatoka Disease and the fungi responsible. Image credit: 10.1371/journal.pgen.1005904

While many fungi are harmful pathogens, that isn’t always a bad thing for humans. The authors of this PLOS Pathogens article demonstrate that spores of the fungus Metarhizium brunneum can adhere to, penetrate, and kill Aedes aegypti larvae [6]. A. aegypti is the mosquito vector of yellow fever, dengue, Chikungunya, Zika, and other diseases; thus this fungus could be a biocontrol mechanism for limiting the spread of disease.

Image credit: Flickr user jentavery
Aedes aegypti feeding. Image credit: Flickr user jentavery

In addition to being pathogens, fungi are also susceptible to infection themselves. A PLOS ONE article describes five new viruses that infect the fungus Cronartium ribicola, which is itself a pathogen responsible for a severe stem canker disease of native white pine trees in North America [7]. Fungi can also be infected by other fungi! In a mind-bending chain of pathogens, the authors of this PLOS ONE paper study a fungus, Ampelomyces, which infects powdery mildew fungus, which is itself a plant pathogen. They find that Ampelomyces is a generalist pathogenic fungus, able to infect multiple diverse hosts [8].

 

Fungi also form non-pathogenic, symbiotic relationships with plants, animals, algae, and other fungi. Indeed, the majority of land plants are dependent on a symbiotic relationship with arbuscular mycorrhizal (AM) fungi, as reviewed in this article in Agronomy [9]. The fungi absorb essential nutrients from the soil and exchange these for carbon metabolites across a specialized plant-fungus interface. Fungi are also a component of the human skin microbiome; indeed, members of the genus Malassezia are the dominant eukaryotic inhabitants of human skin, and in this PLOS Genetics article the authors investigate the genomic features responsible for their unique lipophilic lifestyle [10]. Another fascinating symbiotic relationship is between fungi and ambrosia beetles. These beetles “farm” the fungi, establishing and maintaining fungal colonies on dead wood. The fungi break down the wood and provide food for the beetles. This PLOS ONE article characterizes one of these beetle-fungus symbioses, which reveals several unique features [11].

Image credit: doi: 10.1371/journal.pone.0137689. Arrows point to fungi.
An Ambrosia beetle on its farm. Arrows point to fungal symbionts. Image credit: doi:10.1371/journal.pone.0137689.

Many diverse fungi are able to live part or all of their lives inside plants, and while they impact plant fitness, it’s not clear how they interact with plant cells. In this PLOS ONE paper, the authors propose that some of these endophytes are able to move from within the plant to within the plant cells, which could help to explain their hidden existence, lifestyle switching, and diversity within the plant kingdom [12]. Some aspects of the fungi lifestyle require cooperation and communication amongst similar individuals. This article published in PLOS Biology demonstrates how the filamentous fungus Neurospora crassa is able to recognize genetically similar individual via recognition of “greenbeard genes” [13]. Greenbeard genes allow the fungus to limit helpful behaviors to just those individuals that are most likely to perpetuate their own genetic make-up.

 

Given that fungi diverged from plants and animals hundreds of millions of years ago, they have acquired some unique features. Regulation of the cell cycle is one of the most conserved processes, however many fungi use a protein – known as SBF – in place of E2F, a transcription factor highlight conserved from bacteria to mammals. This eLife article posits that a fungal ancestor acquired a SBF precursor from a viral infection, which hijacked cell cycle control and eventually replaced E2F functionally [14].

 

And this is just the icing on the fungus cake! For more information on UK Fungus Day and events happening all around the UK, check out: http://www.ukfungusday.co.uk/

 

For more detailed reading:

[or see this associated PLOS Collection]

 

  1. Rodríguez-Brenes S, Rodriguez D, Ibáñez R, Ryan MJ (2016) Spread of Amphibian Chytrid Fungus across Lowland Populations of Túngara Frogs in Panamá. PLoS ONE 11(5): e0155745. doi: 10.1371/journal.pone.0155745

 

  1. Seimon TA, Ayebare S, Sekisambu R, Muhindo E, Mitamba G, et al. (2015) Assessing the Threat of Amphibian Chytrid Fungus in the Albertine Rift: Past, Present and Future. PLoS ONE 10(12): e0145841. doi: 10.1371/journal.pone.0145841

 

  1. Ordonez N, Seidl MF, Waalwijk C, Drenth A, Kilian A, et al. (2015) Worse Comes to Worst: Bananas and Panama Disease—When Plant and Pathogen Clones Meet. PLoS Pathog 11(11): e1005197. doi: 10.1371/journal.ppat.1005197

 

  1. Chang TC, Salvucci A, Crous PW, Stergiopoulos I (2016) Comparative Genomics of the Sigatoka Disease Complex on Banana Suggests a Link between Parallel Evolutionary Changes in Pseudocercospora fijiensis and Pseudocercospora eumusae and Increased Virulence on the Banana Host. PLoS Genet 12(8): e1005904. doi: 10.1371/journal.pgen.1005904

 

  1. Arango Isaza RE, Diaz-Trujillo C, Dhillon B, Aerts A, Carlier J, et al. (2016) Combating a Global Threat to a Clonal Crop: Banana Black Sigatoka PathogenPseudocercospora fijiensis (Synonym Mycosphaerella fijiensis) Genomes Reveal Clues for Disease Control. PLoS Genet 12(8): e1005876. doi: 10.1371/journal.pgen.1005876

 

  1. Alkhaibari AM, Carolino AT, Yavasoglu SI, Maffeis T, Mattoso TC, et al. (2016) Metarhizium brunneum Blastospore Pathogenesis in Aedes aegypti Larvae: Attack on Several Fronts Accelerates Mortality. PLoS Pathog 12(7): e1005715. doi: 10.1371/journal.ppat.1005715

 

  1. Liu JJ, Chan D, Xiang Y, Williams H, Li XR, et al. (2016) Characterization of Five Novel Mitoviruses in the White Pine Blister Rust Fungus Cronartium ribicola. PLoS ONE 11(5): e0154267. doi: 10.1371/journal.pone.0154267

 

  1. Pintye A, Ropars J, Harvey N, Shin HD, Leyronas C, et al. (2015) Host Phenology and Geography as Drivers of Differentiation in Generalist Fungal Mycoparasites. PLoS ONE 10(3): e0120703. doi: 10.1371/journal.pone.0120703

 

  1. Bücking, H.; Kafle, A. Role of Arbuscular Mycorrhizal Fungi in the Nitrogen Uptake of Plants: Current Knowledge and Research Gaps. Agronomy 2015, 5, 587-612.

 

  1. Wu G, Zhao H, Li C, Rajapakse MP, Wong WC, et al. (2015) Genus-Wide Comparative Genomics of Malassezia Delineates Its Phylogeny, Physiology, and Niche Adaptation on Human Skin. PLoS Genet 11(11): e1005614. doi: 10.1371/journal.pgen.1005614

 

  1. You L, Simmons DR, Bateman CC, Short DPG, Kasson MT, et al. (2015) New Fungus-Insect Symbiosis: Culturing, Molecular, and Histological Methods Determine Saprophytic Polyporales Mutualists of Ambrosiodmus Ambrosia Beetles. PLoS ONE 10(9): e0137689. doi: 10.1371/journal.pone.0137689

 

  1. Atsatt PR, Whiteside MD (2014) Novel Symbiotic Protoplasts Formed by Endophytic Fungi Explain Their Hidden Existence, Lifestyle Switching, and Diversity within the Plant Kingdom. PLoS ONE 9(4): e95266. doi: 10.1371/journal.pone.0095266

 

  1. Heller J, Zhao J, Rosenfield G, Kowbel DJ, Gladieux P, et al. (2016) Characterization of Greenbeard Genes Involved in Long-Distance Kind Discrimination in a Microbial Eukaryote. PLoS Biol 14(4): e1002431. doi: 10.1371/journal.pbio.1002431

 

  1. Medina EM, Turner JJ, Gordan R, Skotheim JM, Buchler NE. (2016) Punctuated evolution and transitional hybrid network in an ancestral cell cycle of fungi. eLife  5:e09492. http://dx.doi.org/10.7554/eLife.09492

 

 

Featured Image Credit: U.S. Department of Agriculture

 

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