Flipping pulses’ nitrogen fixation “off-switch”/
What a new discovery means for the future of food systems

A genetic “off switch” that shuts down the process in which legume plants convert atmospheric nitrogen into nutrients was identified for the first time by a team of international scientists, led by La Trobe University researchers. The identification of the gene, says Ried, is an important breakthrough that can allow scientists to increase the biological ability of legumes to fix nitrogen and help increase crop growth and yield while also reducing the need for synthetic fertilizers. 

Tell us about your research on nitrogen fixation in legume crops.

• It’s well-known that when you have nitrogen already in the paddock, pulses will fix less nitrogen so we wanted to understand more about the relationship and try to identify new players that might be relevant as targets for improvement. 
• More generally, we were aiming to understand more about the pathways involved so we can eventually manipulate these with the hope of improving nitrogen fixation.

What was your main objective?

• To understand how nitrogen fixation gets shut off. Finding this switch is about finding new options for pulses, putting them in new places where maybe they weren’t optimal previously and making them more attractive to growers.

Can there be too much nitrogen in the soil?

• Nitrogen is very important for plant growth but a legume plant doesn’t ‘need’ to fix nitrogen. If it can get it from the soil, it’s a ‘cheaper’ option for the plant as it doesn’t need to invest in the nodules or the rhizobia that live in the nodules. 
• If there's lots of nitrogen there, legumes plants get lazy and will stop fixing nitrogen. Then we start to lose the benefit both for the soil and for the future crops in the rotation. 

The project is funded by GatesAgOne - how did that relationship come about?

• I’ve been involved in a Gates funded project for about 10 years. Generally, we’ve been looking at trying to transform agricultural productivity by transferring or engineering the ability to fix nitrogen into eg. non-legume crops, which is a bit of a ‘moonshot’ type project. 
• In the course of doing that, however, we’re very interested in understanding more about how legumes control this relationship as it’s a critical part of engineering or reproducing that elsewhere. 
• Gates is particularly interested in this research can translate to cowpeas in Sub Saharan Africa, which is a staple food for more than 200 million people. 

Do Genetically Modified (GM) vs Gene-Edited (GE) distinctions pose challenges?

• Definitions vary globally, but I’m focused on proving concepts rather than the technology. The goal is to make crops more productive and sustainable, regardless of classification. 

Are there any parallels with projects such as Harvest Plus biofortified beans?

• Changing food is more likely to lead to consumer reluctance. We don’t plan to change the fundamental nature of the crop; we’re just trying to make it more sustainable and improve yields, which we hope will drive uptake among farmers. 

Is there any genetic trade-off in enhancing the nitrogen-fixing capabilities of the seed?

• Yes, there’s a balance. We might be able to increase nitrogen fixation by 10-20%, but the optimal yield may come with a smaller increase. Fine-tuning this balance is a key focus.

Are you also looking at increasing the protein content?

• In many crops, the amount of protein in the seed has a strong relationship to nitrogen supply to the plant. Even if we maintain yield but increase protein, that would still be valuable. Or we might maintain protein and yield but increase the amount of nitrogen we leave in the soil. Until we put it in the field and see how it performs, it’s difficult to know. 

What are the main challenges you foresee ahead?

• We’ve identified the relevant gene, so the next challenge is proving that it’s actually useful! We have the resources to test its effectiveness in cowpea, faba bean and soybean over the next three to five years. 
• If successful, we’ll focus on incorporating it into breeding programs as quickly as possible although that represents a new set of challenges. 
• Especially with pulses, a lot of the breeding programs are quite small operations that are dispersed geographically and don't all have resources to implement new targets.