Canadian genomic research furthers quest for plants that make their own fertilizer

In the words of Agriculture and Agri-Food Canada research scientist Dr. Krzysztof Szczyglowski, "It is the Holy Grail" — unlocking the secret behind the ability of some plants to get the nitrogen they need from the air and then transferring that ability to other plants. In other words, plants that fertilize themselves.

Almost 80 percent of Earth's atmosphere is nitrogen. It is one of the basic building blocks of life, present in every cell of every living thing. We cannot survive, let alone thrive, without nitrogen.

That is why the development of nitrogen fertilizers in the last half of the 19th century was such a watershed event. Modern agriculture would not be possible without commercial fertilizers containing nitrogen. It's been estimated that a third or more of today's crop yields can be attributed directly to the application of commercial fertilizers, of which nitrogen is by far the most important. In Canada, for example, nitrogen now accounts for more than 70 percent of the fertilizer used by Canadian farmers, who apply more than four million tonnes of nitrogen fertilizers every year.

Fertilizer is good, but...

Unfortunately, while it would be very difficult to feed the world without it, nitrogen fertilizer also has a substantial downside.

As Dr. Szczyglowski explains, plants fertilized with nitrogen typically use less than half the nitrogen that is applied to the soil. As the use of nitrogen fertilizers has increased, so has the damage it causes to the environment. Excess nitrogen is largely responsible for the algae blooms that have become common in lakes, rivers and coastal waters in Canada and around the world. Nitrogen fertilizers are also the major source of nitrous oxide, a greenhouse gas 300 times more powerful than carbon dioxide. As well, producing nitrogen fertilizer involves burning large amounts of fossil fuels, adding to environmental concern.

Canada part of global effort

Finding a way to reduce or eliminate the need for nitrogen fertilizers without reducing agricultural output is the focus of a major global scientific effort. The Bill and Melinda Gates Foundation, for example, is providing almost $10 million to support research into self-fertilizing cereal crops.

With the support of funding from the Government of Canada's Genomics Research and Development Initiative (GRDI), Dr. Szczyglowski and his team at Agriculture and Agri-Food Canada's (AAFC) Southern Crop Protection and Food Research Centre in London, Ontario, are making important contributions to this global effort.

Fertilizer from the air

"There are about 380 families of flowering plants on Earth," says Dr. Szczyglowski. "Almost all of them must get the nitrogen they need from the soil. But there are members of about 10 families of plants that are able to get nitrogen from the atmosphere — these are mostly legumes, like peas, soybeans and alfalfa."

Dr. Szczyglowski and his colleagues at AAFC, in collaboration with researchers as far afield as Denmark and Japan, have made substantial progress toward understanding how these plants are able to obtain nitrogen from the air.

"The plants we are studying can't actually do this by themselves," explains Dr. Szczyglowski. "When they sense there is not enough nitrogen in the soil, these plants allow what you might call 'friendly soil bacteria' to enter their root cells. While residing within these cells, bacteria fix atmospheric nitrogen so it can be used by the host plant to support its growth and productivity."

A welcome mat for bacteria

This friendly relationship between the plant and the bacteria is unusual, to say the least, since living cells have elaborate mechanisms designed specifically to keep bacteria out.

The genetic analyses performed by Dr. Szczyglowski and his team have identified parts of the plant's genetic apparatus that act as a sort of command centre. This command centre tells other genes how to act in order to recognize the friendly bacteria, and when and how to let them enter the plant's root cells. Dr. Szczyglowski's team has also identified the one gene that initiates a process known as root nodule morphogenesis — essentially, the process by which the root cells change to accommodate the friendly bacteria.

Exciting possibilities

Perhaps most exciting is the discovery that at least part of the genetic process that allows legumes to interact with bacteria in order to get nitrogen from the air is used by many other plants to interact with friendly fungi in order to obtain phosphate, another key nutrient.

"Much more work is needed, but this discovery reinforces our belief that it will be possible to transfer the nitrogen-fixing process used by legumes to other important food crops," says Dr. Szczyglowski. "The implications are enormous — developed countries would be able to reduce their use of nitrogen fertilizers, while poorer countries, where farmers cannot afford commercial fertilizer, would be able to increase food production."

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