In the quest to make agriculture more sustainable and reduce its reliance on synthetic fertilizers, a fascinating discovery has emerged from the laboratories of the All-Russia Research Institute for Agricultural Microbiology (ARRIAM) in St. Petersburg. Led by Anton S. Sulima, a team of researchers has delved into the genetic secrets of peas, unveiling a mechanism that could revolutionize how we think about plant-microbe symbiosis and its potential to transform the agricultural landscape.
Peas, a staple crop and a crucial component of crop rotation, have long been known for their ability to fix nitrogen through symbiotic relationships with rhizobia, bacteria that convert atmospheric nitrogen into a form usable by plants. This natural process not only enriches the soil but also reduces the need for nitrogen-based fertilizers, which are energy-intensive to produce and contribute to greenhouse gas emissions.
The key to this symbiosis lies in the pea’s ability to selectively interact with certain strains of rhizobia. The gene Sym2 plays a pivotal role in this process, determining the specificity of the interaction. Peas with the Sym2A allele, found in landraces from Afghanistan, are highly selective and can only form nodules with rhizobia that possess a specific gene, nodX. In contrast, European cultivars with the Sym2E allele are less discriminating and can interact with a broader range of rhizobia.
Sulima and his team focused on an introgression line, A33.18, which carries the Sym2A allele in a homozygous state within the genome of the European pea cultivar ‘Rondo’. This line was created to test the hypothesis that introducing the Sym2A allele could enhance the specificity of symbiosis, giving peas a competitive edge in forming nodules with beneficial rhizobia.
“Our goal was to see if we could create a pea that could selectively interact with a specific strain of rhizobia, thereby improving the efficiency of nitrogen fixation and reducing the competition from indigenous soil microbiota,” Sulima explains.
The results were striking. In field experiments, when inoculated with the nodX+ strain TOM, over 95% of the nodules formed on A33.18 peas contained TOM, compared to less than 8% in the parental cultivar ‘Rondo’. This high selectivity suggests that the introgression of Sym2A enables peas to interact specifically with the desired strain, protecting them from less beneficial indigenous soil microbiota.
The implications of this research are profound. By enhancing the specificity of the symbiotic relationship, farmers could potentially use biofertilizers based on selected, highly effective rhizobia strains. This would not only reduce the reliance on synthetic fertilizers but also create a more sustainable and energy-efficient agricultural system.
The research, published in the journal Plants, opens up new avenues for genetic modification and breeding programs. Sulima envisions a future where CRISPR/Cas9 editing could further refine the specificity of the interaction, making it even more precise and effective. “The ability to edit the LykX gene, which is a candidate for Sym2, could lead to even more selective and efficient symbiosis,” he says.
As the world seeks to transition to more adaptive and sustainable agricultural practices, this discovery could be a game-changer. By harnessing the power of plant-microbe symbiosis, we could reduce the energy footprint of agriculture, improve soil health, and ultimately contribute to a more sustainable future. The research by Sulima and his team at ARRIAM is a significant step forward in this direction, offering a glimpse into the potential of genetic engineering to transform agriculture.