In pursuit of the white lupine

Like Alice chasing the white rabbit in Wonderland, biologist Benjamin Péret's team has been chasing the white lupine for the past five years.
A plant capable of capturing nutrients even in very poor soils, which could help prevent a future phosphate crisis. The sequencing of its genome, carried out for the first time at the BPMP laboratory in Montpellier, has identified the gene responsible for this astonishing power.

If Alice's white rabbit was "always late"The white lupin seems to be one step ahead of the other plants in our gardens. Recognized by its large clusters of white flowers, or multicolored in its ornamental version, this leguminous plant has until now been best known for the crunchiness of its seeds, served as an appetizer. Today, it's its roots that are of interest to the scientific community, and in particular to Benjamin Péret, a researcher at the Biochemistry and Molecular Physiology of Plantes (BPMP). "Some lupins have the extraordinary ability to develop what we call proteoid roots. This is a specificity found in very few plants", explains the biologist. Short, dense roots capable of capturing nutrients more efficiently, especially phosphate, even in very poor soils.

Extraordinary roots

Phosphate is an essential nutrient for plant growth, but is difficult to capture. "Even if phosphorus is present in large quantities in the soil, it is not always in a form that can be assimilated by plants. It is estimated, for example, that 80% of the phosphate contained in fertilizer cannot be recovered. Lupins are much more efficient. How can it do this? Thanks to a specific root system capable of secreting enzymes designed to break down phosphate from organic molecules, making it available to plants. " In phosphate-rich soil, lupins will produce very few proteoid roots, whereas in poor soil, they will develop many," adds the biologist.
This direct response of the organism to its environment is typical of plants, as Laurence Marquès, also a member of the Development and Plasticity of the Root System team, points out: "Animals or humans are not capable of adapting their organs or limbs to the environment, whereas in plants there is this plasticity that enables direct interaction." To go a step further, the biologists set out to identify the gene responsible for the development of these astonishing roots. "We want to understand how the plant transforms the phosphate signal into a molecular signal and then into a developmental response," explains Benjamin Péret.

The first genome sequencing

With the collaboration of eleven French and European research laboratories, including the Toulouse bioinformatics platform, Benjamin Péret's team was the first to sequence, assemble and make public the 38,528 genes of the lupin genome. A success in itself, but the gene responsible for the formation of these proteoid roots had yet to be unmasked.
This is where mutants come in. "All plants naturally produce mutants. It's an evolutionary engine that allows new functions to appear over thousands of years, thanks to new genes". Since Mother Nature's timing is not that of science, the researchers used various processes to increase the natural mutation rate, and were thus able to select 4 mutants out of the 25,000 tested. No magic beans or flowers with speech in this story, but simple lupins with overdeveloped proteoid roots.
By comparing the genome of these mutants with that of an ordinary lupin, Benjamin Péret's team succeeded in identifying the gene which, by mutating, had triggered the development of these roots. "We found that when the function of this gene is lost because it has been mutated, lupin plants make even more proteoid roots. These mutants are fantastic tools for trying to understand the mechanism of formation of these extraordinary roots."

Preventing the phosphate crisis

Thanks to the localization of this gene, the identity of which is still a secret, biologists envisage a possible transfer to field crops, which would then develop the same roots as lupins, with major phosphate savings at stake. The stakes are high when you consider that phosphate, extracted from mines located mainly in Morocco and China and a mainstay of world agriculture, could run out in the next few decades, raising the risk of an unprecedented food crisis, warns Benjamin Péret: "Phosphate is not like oil, there is no possible alternative.