Symbiotic Relationship: Legume Roots Have Protein That Help Them Find Their Partner Bacteria

Legumes are plants that produce pods with seeds inside. Common legumes are peas, beans, and various species of clover. They need organic nitrogen to grow, which they get from the air or the bacteria in the soil using their specialized structure in the roots.

Researchers from the University of Freiburg's Faculty of Biology led by cell biologist Prof. Dr. Thomas Ott have detected and identified a factor in the roots of legumes that help it associate with the soil bacteria it needs.

Together with other scientists, the team published their study, entitled "Formin-mediated bridging of cell wall, plasma membrane, and cytoskeleton in symbiotic infections of Medicago truncatula," in the journal Cell Biology.

Symbiotic Relationship of Legumes and Bacteria

According to Trees for Life, symbiosis comes from the Greek word "living together." Scientists have been using this term to talk about parasitism, commensalism, and mutualism among organisms like plants and animals.

For example, legumes have a symbiotic relationship with nitrogen-fixing bacteria. Legumes need nitrogen to grow, while it releases nutrients and energy for the bacteria. These organisms have a mutualistic relationship because they both benefit from each other.

That means nitrogen fixation is a symbiotic relationship between a plant and a bacterium, which involves the latter invading the roots of the former and multiply within its cortex cells.

According to an article published on the website of the New Mexico State University, small nodules would appear after two to three weeks of planting. At first, they would be white and gray but it then turns red or pink when it is already fixing nitrogen.

So how do legumes find these nitrogen-fixing bacteria that help them grow? Researchers might now have the answer to that.

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SYFO1 In Roots Finds Symbiotic Partner for Plants

Dr. Ott's team found a factor in roots that the plants need for the initial contact with the nitrogen-fixing bacteria that live in the soil. These proteins are called symbiotic forming 1 (SYFO1) that are exclusive to legumes and play a significant role in symbiosis.

Phys.org reported that when a bacterium enters the roots of legumes, the SYFO1 protein is activated which causes tiny hairs of the root to change the direction of their growth. They wrap themselves around the symbiotic partner which allows legumes to grow even without nitrogenous fertilizers.

"If we understood precisely how the symbiosis comes into being, we could give crop plants back this special property they have lost in the course of evolution," says Ott.

The team used the roots of the legume barrel medic (Medicago truncatula) in their study to demonstrate that the root hairs of the plants to which SYFO1 has been switched off can not wrap themselves around the nitrogen-fixing bacteria.

Further studies also reveal that SYFO1 binds to actin and at the cell wall outside the cells, which causes the plant's direction of growth to change.

Ott noted that SYFO1 only responds to symbiotic signals from the bacteria and that learning about them constitutes a special innovative step in plant evolution.

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