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Stress relief for crops

These bacterial endophytes may give farmers more control over their crops than anyone has ever dreamed could be possible

In the chase to increase agricultural productivity, science has turned to hybridization, transgenics, soil fertility, pest resistance and even CRISPR. Every year there’s been something new. So what more could there be left to explore?

Well, what if we could effectively stop stress? How much would our yields go up if stress was no longer a limiting factor?

Dr. Trevor Charles is working to answer those questions, and his primary method is to decrease stress response via plant growth-promoting bacterial endophytes.

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It’s very scientific, but the concept is fairly straightforward. First, we need to know a bit about ethylene, one of the five major plant hormones that regulate plant growth, and the only one that exists as a gas.

Ethylene can also be produced in almost any part of a plant, and because it is a gas, once it has been emitted, it has the capability of affecting neighbouring plants too.

It turns out that some bacterial endophytes (those that contain the enzyme ACC (1-aminocyclopropane-1-caboxylate deaminase) can alter the ability of plants to produce ethylene.

Now a professor at the University of Waterloo, Charles began working with Dr. Bernie Glick who had developed a method of identifying bacteria that could promote the growth of plants. The ones Charles is particularly interested in are those that can alter the ability of the plants to produce ethylene.

“Under stress conditions, you find that a lot of plants will produce spikes of ethylene — called stress ethylene,” says Charles. “This signals that plant and all of the surrounding plants to respond to that stress. In many cases, they will reduce their growth or do things like start senescence — start aging.”

Some bacteria, however, will short-circuit the production of ethylene by metabolizing a molecule called ACC (1-aminocylcopropane-1 — carboxylate), which is its immediate precursor.

With his spinoff company Metagenom Bio, Charles is researching bacteria that work well as inoculants with vegetables and specialty crop production, mainly for controlled-environment agriculture. “You’re not going to see corn and soybeans grown in a greenhouse or an indoor farm, but you are going to see vegetables of all types,” Charles says.

“In Canada, half of the vegetables are produced in greenhouses. These are hydroponic systems where there’s the potential to precisely engineer the system, giving the plants exactly what they want.”

Does that mean there’s no interest in helping growers of row crops improve their production?

Not at all. In fact, in a research paper published in April 2014, growth promotion through the use of ACC deaminase was tested in tomatoes (under high salinity conditions). Tests were conducted in canola but the only data gathered from that relates to root elongation and hasn’t been transferred from the greenhouse to the field.

For now, the vegetable market provides the scale and the cost-effectiveness to attract endophyte and ACC deaminase development, but there’s also growing interest in finding plant growth-promoting bacteria that work well in corn, soybeans and canola, particularly given their volume-based production.

Enhancing the microbiome

The soil is getting more research attention, but Charles still believes that optimizing the soil microbiome has been too neglected.

From a bioengineering perspective, Charles asks if it’s possible to enhance the microbiome to optimize for maximum yield while reducing the length of the growing season or changing the light or nutrient requirements. There is research currently underway working with irrigation systems to distribute inoculant organisms, and Charles agrees there’s a huge potential for using irrigation to rebalance the microbiome.

“Salinity is interesting and something that we find with some of our strains, that we can get tomato plants to grow and produce quite well in a salt equivalent to one-third the concentration of seawater,” he notes. “That could really open up a lot of land that is not currently good for growing much.”

Admittedly, salinity isn’t a huge factor for growers in Eastern Canada, although it does have an impact on production in the West. Charles has found that it’s also a concern in greenhouse vegetable production, particularly in hydroponics where nutrient solution is recirculated to the point where it can develop a higher salinity concentration.

Silver lining

One interesting discovery is that many of the bacterial strains that have the ACC deaminase trait are also able to produce indoleacetic acid (IAA), which is important in promoting cell growth. The challenge is that such cell-growth promotion often comes at the expense of a stress ethylene spike, meaning the ACC deaminase trait can be counteracted by IAA.

“The hypothesis is that those traits sort of ‘play’ together, that as IAA is causing the cells to grow, the ACC deaminase is keeping the resulting ethylene lower so that plants can respond with a yield increase,” says Charles. “If the bacteria cause the plants to ramp up their ethylene synthesis, the plants are actually producing the ACC which can be used as a nitrogen source for the bacteria. In a way, it’s self-sufficient.”

Charles has also been conducting research into the use of endophytes under different light conditions. He’s hypothesized that under low-light conditions, there might be a better response from the addition of endophytes.

Slow regulatory response

From a regulatory perspective, the response to Charles’s work has been slow but positive. He echoes the statements of many Canadian researchers and innovators about the time factor involved in regulatory submissions through Health Canada and the Canadian Food Inspection Agency (CFIA). Charles notes that it’s unusual that a naturally occurring bacterium with plant growth-promoting properties would have to go through regulatory approval. In many parts of the world, a product that’s naturally occurring would not require registration.

“We actually received very little feedback about the evaluation,” says Charles, adding that it was 18 months after submission that he found out it had been approved. “The frustrating part of it — and we knew this would be the case — was the amount of data required in the submission and also the amount of time it takes, which is really a challenge for innovation.”

Help on the horizon

What may help in the long run is Charles’s involvement with two networks: the International Phytobiomes Alliance and MicrobiomeSupport. The International Phytobiomes Alliance is a research-based organization that has both academic researchers and private sector companies focused on the microbiome of plants.

“From our knowledge of the microbiome and our ability to figure out how to improve it, we want to know how to get plants to grow better and produce more, with less impact on the environment,” says Charles. “We’re actually leading the controlled environment agriculture working group on that and trying to get some funding.”

Both organizations unite scientific and corporate interests in a collaborative effort, a paradigm shift that acknowledges more can be done when public and private sectors work together.

“Actually, that’s one of the reasons that these organizations are so important,” says Charles. “They provide a forum for businesses to get together and communicate in a less-competitive environment, thanks in part to the academics working with them.”

About the author

CG Production Editor

Ralph Pearce



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