Nature’s most widespread and longest-lasting symbiotic relationship shows green promise for agriculture and biotechnology

  • 08
  • JUN
  • 2017

One of biology’s most charismatic relationships, credited with helping plants to colonise land more than 400 million years ago, has yielded a fundamental survival secret with implications for agriculture and biotechnology.

Plant scientists have discovered that a particular form of fungi, which invades plant roots and then helps the colonised plants to absorb nutrients from soil, receive life-sustaining carbon from their symbiotic hosts in the form of long-chain fatty acids, a building block for essential lipids.

Previously, scientists had thought that the fungi received carbon from their hosts only in the form of carbohydrates, which the fungi used to make their own fatty acids and then the more complex lipids necessary for survival.

It’s now clear that the main source of carbon from the host plants are fatty acids, and that these fatty acids are necessary before the fungi can create the more complex lipids that are needed for storing energy, for signalling and for cellular membranes.

The latest work, published online today [7pm BST, Thursday, 8 June 2017] by Science, comes from a joint team of scientists from Rothamsted Research and the John Innes Centre. This field of science is very competitive currently, with research groups in China, Germany and the US all chasing similar breakthroughs.

“This is exciting biology. We’ve discovered that the fungus is effectively re-programming the plant to pump out lipids,” says Peter Eastmond, senior biochemist in the Department of Plant Sciences at Rothamsted and co-leader of the research team.

“There are important implications for sustainable agriculture, particularly in nutrient-poor soils where you need to make the most of resources,” says Eastmond. “And also for biotechnology, in creating green pathways to produce lipids in plants, for biofuels and for precursor chemicals for industrial applications, as an alternative to fossil fuels.”

The symbiotic relationship at the heart of this research, and one of the most widespread associations in nature, is that between the great majority of plants, at least 80% of them, and arbuscular mycorrhizal fungi, which create special feeding structures within the plants’ roots called arbuscules. (TOP: Microscopy image (x200) shows fungal arbuscules (green blocks, about 60 micrometers long) and hyphae (green tubes) containing lipid drops (red spots) inside the plant root (background); ABOVE: Legumes, such as this crop of field (broad) beans, are among the many plants capable of developing symbiotic associations with arbuscular mycorrhizal fungi in the soil.)

The fungi, which develop hyphae to increase the roots’ surface area, can provide the plant with up to 80% of its nutrients from soil while the plants can yield up to 30% of the carbon they derive through photosynthesis to the fungi.

Rothamsted began to investigate the relationship’s metabolism in 2011 after ground-breaking genetic studies at the JIC had been the first to identify and isolate two genes essential for sustaining the symbiosis, RAM (Required for Arbuscular Mycorrhization)1 and RAM2.

“We grappled with understanding why these genes were so important until we came up with the hypothesis that the symbiosis created a lipid factory in the plant that fed the fungus,” recalls Eastmond. “This went against what the literature said...we were proposing to overturn what’s in the text books.”

But this is what they did. The team came up with a trio of robust and ingenious experiments that got around the inseparable union to distinguish whether one or both of the symbiotic partners were producing lipids. Each experiment independently endorsed the hypothesis. 

“There’s a lot more work to do in following up this discovery,” says Eastmond. “It will have a lasting impact on the understanding of the metabolism of this symbiotic relationship and lead researchers in many new directions.”

Giles Oldroyd, project leader in cell and developmental biology at JIC, and co-leader of the research team comments: “It has long been thought that the plant delivered sugars to the symbiotic fungi. Our research demonstrates that in addition the plant delivers lipids to the fungus...We hope that through a better understanding of these plant/fungal symbioses we may be able to improve their use in agriculture and thus increase the sustainability of agricultural systems.”

John Innes Centre contacts:

For alternative access to paper, contact The SciPak Team at Science magazine:

About Rothamsted Research
Rothamsted Research is the longest-running agricultural research institute in the world. We work from gene to field with a proud history of ground-breaking discoveries, from crop treatment to crop protection, from statistical interpretation to soils management. Our founders, in 1843, were the pioneers of modern agriculture, and we are known for our imaginative science and our collaborative influence on fresh thinking and farming practices.
Through independent science and innovation, we make significant contributions to improving agri-food systems in the UK and internationally. In terms of the institute’s economic contribution, the cumulative impact of our work in the UK was calculated to exceed £3000 million a year in 20151. Our strength lies in our systems approach, which combines science and strategic research, interdisciplinary teams and partnerships.
Rothamsted is also home to three unique resources. These National Capabilities are open to researchers from all over the world: The Long-Term Experiments, Rothamsted Insect Survey and the North Wyke Farm Platform.
We are strategically funded by the Biotechnology and Biological Sciences Research Council (BBSRC), with additional support from other national and international funding streams, and from industry. We are also supported by the Lawes Agricultural Trust (LAT).
For more information, visit; Twitter @Rothamsted
1Rothamsted Research and the Value of Excellence: A synthesis of the available evidence, by Séan Rickard (Oct 2015)

The Biotechnology and Biological Sciences Research Council is part of UK Research and Innovation, a non-departmental public body funded by a grant-in-aid from the UK government.
BBSRC invests in world-class bioscience research and training on behalf of the UK public. Our aim is to further scientific knowledge, to promote economic growth, wealth and job creation and to improve quality of life in the UK and beyond.
Funded by government, BBSRC invested £469 million in world-class bioscience in 2016-17. We support research and training in universities and strategically funded institutes. BBSRC research and the people we fund are helping society to meet major challenges, including food security, green energy and healthier, longer lives. Our investments underpin important UK economic sectors, such as farming, food, industrial biotechnology and pharmaceuticals.
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About LAT
The Lawes Agricultural Trust, established in 1889 by Sir John Bennet Lawes, supports Rothamsted Research’s national and international agricultural science through the provision of land, facilities and funding. LAT, a charitable trust, owns the estates at Harpenden and Broom's Barn, including many of the buildings used by Rothamsted Research. LAT provides an annual research grant to the Director, accommodation for nearly 200 people, and support for fellowships for young scientists from developing countries. LAT also makes capital grants to help modernise facilities at Rothamsted, or invests in new buildings.