This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Scientists have taken a step toward a better understanding of how fungi sense and respond to nutrients in the environment, which is critical for engineering fungi for green technologies and combating fungal pathogens and their resistance to treatments. Fungal diseases can contribute to up to 20% of staple crop losses before and after harvest, and rising drug-resistant fungal infections in humans can lead to roughly 3.8 million deaths globally each year.
A new study, published Sept. 1 in PLOS Biology, identified a transcription factor—a protein that turns genes on and off and regulates which genes are expressed—called Cbr1 in the single-celled fungus Rhodotorula toruloides. Cbr1 regulates genes involved in breaking down complex sugars into glucose, making the carbon more accessible as food by activating the genes' expression and bypassing a negative feedback loop that would otherwise repress genes that facilitate the use of complex sugars. Unraveling how fungi sense nutrients helps scientists gain insight into environmental nutrient cycling, as fungi are key decomposers that return nutrients from plant biomass to the soil.
It also helps identify important targets for treating diseases caused by pathogenic fungi. "The fungus in this paper is not a serious pathogen, but many fungi are, for either plants or animals. We know that if we modulate their ability to sense and respond to nutrients, we can disrupt them," said Lori Huberman, assistant professor in the Plant Pathology and Plant-Microbe Biology Section in the School of Integrative Plant Science (SIPS) in the College of Agriculture and Life Sciences.
Co-first authors include Brandon Reyes-Chavez, a graduate student, and Joshua Kerkaert, a postdoctoral associate, both in Huberman's lab. R. toruloides also has potential as a replacement for petroleum, as it accumulates up to 70% of its biomass as lipids (fats). People are currently working to metabolically engineer the organisms to take those lipids and direct them toward making other useful molecules, Huberman said, such as environmentally friendly plastics or biofuel.
"These yeasts that we studied are able to eat all of the breakdown products of the plant cell, so they can be fed grasses grown on marginal lands or agricultural waste," Huberman said. "We can give them waste and they can utilize that." R. toruloides feeds on carbon found in plant tissue, and the most accessible form of that carbon is glucose, with each molecule containing six carbon atoms. "Fungi always want to eat the best mix of sugars for them," Huberman said.
"The thing they most like to eat is glucose, so if there is glucose around, the fungi are going to repress the expression of genes that are necessary to utilize carbon sources that require more energy." In the study, the team used a technique called transcriptomics, which allowed them to measure gene expression for all the genes in R. toruloides' genome and in the genomes of strains of R. toruloides that the researchers had engineered. The technique allowed them to identify genes regulated by Cbr1. One of those genes expresses an enzyme that breaks down a plant sugar called cellobiose, which is made up of two molecules of glucose, the most desirable food source for fungi.
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