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Fungi used in bio-fertilizer reproduce through sex

by Lindsay Jolivet Apr 28 / 16

Researchers have dissected the genetic makeup of a fungus used as fertilizer in organic farming, which could help produce better strains for better crops.

Arbuscular mycorrhizal fungi (AMF) live with most plants on earth. They are an important ally, helping plants absorb more nutrients from the soil than they can using their roots alone, says Nicolas Corradi (University of Ottawa), a CIFAR fellow in the Integrated Microbial Biodiversity program.

“Roots allow the plants to gather nutrients up to a certain soil depth. The fungi attach themselves to those roots and extend little arms — we call them hyphae — and that allows the plants to reach nutrients much, much deeper,” he says. In return, the plant provides AMF carbon it fixed through photosynthesis.

The fungus is widely used as a bio-fertilizer but its genetics are poorly understood. “AMF has, for a very long time, been frustrating for scientists because they have a very bizarre cellular system,” Corradi says. Most organisms have one nucleus inside each cell, but AMF has hundreds of nuclei floating around inside each cell. Researchers have theorized for years about how AMF reproduces, with or without sex.

One theory suggested that its many nuclei could all be genetically different from each other — like a metagenome within its cells. This peculiar structure would allow it to produce genetically different offspring without a mate.

The reality is much more ordinary. Through genomic sequencing and analysis, Corradi and his team found that AMF shows all the signs of reproducing through sex. They found two distinct sets of nuclei inside its cells — one from each parent — and two genes that look much like those related to mating in other fungal species.

Run-of-the-mill sexual reproduction might be genetically boring, but it could be great for environmental applications in farming and soil. “We know how the mechanism works now,” Corradi says. Understanding the genome opens the door to studying why some strains of AMF help plants grow better than others. Then, researchers could potentially improve upon nature. Corradi says his lab wants to observe AMF reproduction to verify the molecular signs they’ve already found. A deeper understanding of AMF also sheds light on how plants evolved from aquatic environments hundreds of millions of years ago. AMF is thought to have helped them take root on dry land.

Corradi says the research ties into the goals of CIFAR’s Integrated Microbial Biodiversity program.

“Integrated Microbial Biodiversity works on many different aspects of microbial biodiversity, and one of those aspects is fungal diversity and how this fungal diversity may improve the economy in general, particularly what we call the green economy,” he says.

The research is published in Nature Microbiology.