Comparative genome mining of endophytic Aspergillus species reveals conserved biosynthetic gene clusters across multiple hosts
This study presents the first comparative genomic analysis of endophytic *Aspergillus fumigatus* and *Aspergillus terreus* isolated from Iranian medicinal plants, revealing a high diversity of conserved and species-specific biosynthetic gene clusters that highlight their exceptional metabolic potential for natural product discovery.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Deep within the healthy tissues of plants, invisible to the naked eye, lives a hidden world of fungi. These are not the molds that rot fruit or the mushrooms that dot the forest floor; they are endophytes, microscopic residents that live inside a plant without making it sick. For decades, scientists have suspected that these hidden guests are chemical factories, producing unique compounds that help the plant survive drought or fight off pests. Among the most prolific of these microscopic residents are species of Aspergillus, a genus of fungi found almost everywhere on Earth. While some Aspergillus species are known to cause disease in humans or spoil food, others live peacefully inside plants, and researchers are increasingly interested in what chemical secrets they might hold. The big question is whether the specific plant a fungus lives in changes the chemicals it makes, or if the fungus carries a standard set of chemical tools regardless of its home. Understanding this relationship is crucial for finding new medicines, as many life-saving drugs, from antibiotics to cholesterol-lowering treatments, were originally discovered in fungi.
In a recent study, researchers in Iran set out to explore this relationship by looking at two specific types of Aspergillus fungi found inside three different medicinal plants. The team focused on Aspergillus fumigatus and Aspergillus terreus, two species known for their ability to produce complex chemicals. They collected samples from the leaves of camel thorn and hollyhock, as well as the roots of salt cedar, all native to the East Azerbaijan region. By carefully sterilizing the plant surfaces and growing the fungi in the lab, they confirmed that A. fumigatus was a true generalist, found living inside all three different plants and in both leaves and roots. In contrast, A. terreus was more selective, appearing only in the salt cedar roots and camel thorn leaves, but completely absent from the hollyhock. This difference in where the fungi were found suggested that A. fumigatus is highly adaptable, while A. terreus might be pickier about its host.
To understand why these fungi behave differently, the researchers turned to a technique called genome mining. Instead of growing the fungi to see what chemicals they produce in a dish, they looked directly at the genetic blueprints, or genomes, of the two species. They used a specialized computer program to scan the DNA for "biosynthetic gene clusters." These are groups of genes that work together like a factory assembly line to build specific chemical compounds. The analysis revealed a striking difference in the potential of these two fungi. The genome of A. fumigatus contained 44 of these gene clusters, while A. terreus possessed a massive 73. This high number for A. terreus is among the highest ever recorded for a fungus living inside a plant, suggesting it has an extraordinary capacity to create a wide variety of chemical compounds.
When the researchers compared the gene clusters of the two species, they found that 15 of them were shared between both. These common clusters likely produce essential tools for survival, such as siderophores, which are molecules that help the fungus grab iron from the plant environment, a nutrient that is often scarce. They also shared genes for terpenes, which are volatile chemicals that can help with communication or defense. However, the differences were just as important. A. fumigatus had unique gene clusters for making fumagillin, a compound known to stop blood vessel growth, and gliotoxin, which affects the immune system. A. terreus, on the other hand, carried the specific genetic instructions for making lovastatin, a famous drug used to lower cholesterol, as well as terreic acid. The study showed that while both fungi share a basic toolkit for living inside plants, they have evolved distinct specializations, with A. terreus appearing to have a much larger and more diverse chemical workshop than its counterpart.
The researchers also noted that the absence of A. terreus in the hollyhock plant might be due to the plant's own chemical defenses, which could inhibit this specific fungus while allowing the more adaptable A. fumigatus to thrive. Although the study identified the genetic potential for these chemicals, the author cautioned that having the genes does not guarantee the fungus is currently making the compounds; many of these genetic factories remain silent unless triggered by specific conditions. Nevertheless, the findings confirm that these endophytic fungi are rich sources of biological diversity. By mapping out the genetic potential of fungi from Iranian medicinal plants, the study highlights them as promising candidates for future drug discovery, offering a glimpse into the vast, hidden chemical library that plants and their microscopic partners share.
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