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A relatively unknown fungus, accidentally found growing on an Acacia tree in the Northern Cape, has emerged as a voracious wood-munching organism with enormous potential in industries based on renewable resources.

The first time someone took note of Coniochaeta pulveracea was more than two hundred years ago, when the South African-born mycologist Dr Christiaan Hendrik Persoon mentioned it in his 1797 book on the classification of fungi.

Now C. pulveracea has had its whole genome sequenced by microbiologists at Stellenbosch University (SU) in South Africa, and henceforth made its debut in cyberspace with a few tweets and a hashtag. All because this relatively unknown fungus has an extraordinary ability to degrade wood – hence the descriptor “pulveracea”, meaning powdery.

In the age of biotechnology, biofuels and the usage of renewable raw materials, this is an important fungus to take note of, says Prof Alf Botha, a microbiologist in the Department of Microbiology at SU.

Over the past 25 years, there has been a number of reports on the ability of species in the Coniochaeta genus to rapidly degrade lignocellulose into fermentable simple sugars. But thus far Prof Botha‘s lab is the only one to be working on C. pulveracea.

The work started in 2011, when he quite randomly snapped a brittle twig, covered in lichen, from a decaying Acacia tree. At the time, he was holidaying with family on a farm in the Northern Cape. “At the time we were looking for fungi and yeasts that can break down wood, so I knew this was something special when I decided to keep the twig,” he explains. But to date, despite numerous attempts, they have not been able to find it again.

However, back in the lab there was great excitement when they observed that this species in the Coniochaeta genus was literally munching its way through birchwood toothpicks. Even more astounding was its ability to change form between a filamentous fungus and a yeast, depending on the environment.

“This is highly unusual for a fungus. We’d typically expect this kind of behavior from some fungal pathogens,” explains Botha.

Over the past decade Botha and his postgraduate students focused on unraveling this yeast-like fungus’ behavior. In 2011 Dr Andrea van Heerden found that it produced enzymes that degraded the complex structures of wood into simple sugars, feeding a community of surrounding fungi that do not have the ability to degrade wood. In 2016, she published the results of her investigation into its ability to switch to a yeast-like growth. Understanding this process would be important to the potential use of this fungi in industrial processes.

In the latest study, MSc student CJ Borstlap worked with Dr Heinrich Volschenk, an expert molecular biologist, and Dr Riaan de Witt from the Centre for Bioinformatics and Computational Biology at SU, to produce the first draft genome sequence of C. pulveracea. With a genome size of 30 million nucleotides and over 10 000 genes, this was no easy task. In the process he picked up the necessary coding skills to identify and name all 10 053 genes, and to identify those responsible for the wood-degrading character of the fungus.

Dr Volschenk says the next step is to understand the fungus’ mechanism of breaking down wood and producing sugars on a molecular level: “With the genetic blueprint now available, we can study the network of genes and proteins the fungus employs to convert wood and other similar renewable resources into more valuable products,” he explains.

The sequence data for C. pulveracea have been deposited at the DNA Data Bank of Japan (DDBJ), the European Nucleotide Archive (ENA) at Cambridge, and GenBank in the United States of America, under the accession number QVQW00000000 and is freely available to all researchers in this field.

Read the paper: Microbiology Resource Announcements

Article source: Stellenbosh University

Image credit: Heinrich Volschenk

Scientists at the Max Planck Institute for Plant Breeding Research in Cologne have revealed that direct physical associations between plant immune proteins and fungal molecules are widespread during attempted infection. The authors’ findings run counter to current thinking and may have important implications for engineering disease resistance in crop species.

Fungal diseases collectively termed powdery mildew afflict a broad range of plant species, including agriculturally relevant cereals such as barley, and result in significant reductions in crop yield. Fungi that cause powdery mildew deliver so-called effector molecules inside plant cells where they manipulate the host’s physiology and immune system. In response, some plants have developed Resistance (R) genes, usually intracellular immune receptors, which recognize the infection by detecting the fungus’ effectors, often leading to plant cell death at the site of attempted infection to limit the spread of the fungus. In the prevailing view, direct recognition of effectors by immune receptors is rather a rare event in plant-pathogen interactions, however, and it has been thought instead that in most cases recognition proceeds via other host proteins that are modified by the pathogen.

In barley populations, one of the powdery mildew receptors, designated mildew locus a (Mla), has undergone pronounced diversification, resulting in large numbers of different MLA protein variants with highly similar (>90%) DNA sequences. This suggests co-evolution with powdery mildew effectors, but the nature of the evolutionary relationship and interactions between immune receptor and effectors remained unclear.

To address these questions, Isabel Saur, Saskia Bauer, and colleagues from the department of Paul Schulze-Lefert first isolated several effectors from powdery mildew fungi collected in the field. Except for two, these proteins were all highly divergent from one another. When the authors expressed the effectors together with matching MLA receptors this led to cell death not only in barley but also in distantly related tobacco cells, already suggesting that no other barley proteins are required for recognition. Using bioluminescence as a marker for direct protein-protein interactions, the scientists indeed found specific associations of effector-MLA pairs in extracts of tobacco leaves. Similarly, a protein-protein interaction assay in yeast also revealed interactions only of matching effector-MLA pairs. These results suggest that highly sequence-related MLA receptor variants directly detect unrelated fungal effectors.

Plant disease is a major cause of loss of yield in crops. Transfer of plant R genes between species is a potentially powerful approach to generate disease-resistant crops. The authors’ discovery that multiple variants of the same resistance gene are able to bind dissimilar pathogen proteins, also in distantly related plant species, underlines the potential of this approach and chimes in with the earlier finding that wheat versions of Mla, Sr33 and Sr50, provide disease resistance to the stem rust isolate Ug99, a major threat to global wheat production.

Paul Schulze-Lefert sees further exciting applications on the horizon: “Our discovery that direct receptor-effector interactions are widespread for MLA receptors suggests that it may be feasible to rationally design synthetic receptors to detect pathogen effectors that escape surveillance by the plant immune system.”

Read the paper: eLife

Article source:Max Planck Institute for Plant Breeding Research

Image credit: Takaki Maekawa