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How Plants Find Their Symbiotic Partners

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What would it be like to produce fertilizer in your own basement? Leguminous plants, like peas, beans and various species of clover, obtain organic nitrogen they have for his or her growth from symbiotic soil bacteria via specialized structures in their roots. A team led by the cell biologist Prof. Dr. Thomas Ott from the University of Freiburg’s Faculty of Biology has now detected a factor in root cells that the plants need for the initial contact with these so-called root-associated bacteria, which live in soil. They found a protein found only in legumes called symbiotic formin 1 (SYFO1) and demonstrated the essential role it plays in symbiosis. Along side the biologist Prof. Dr. Robert Grosse University of Freiburg’s Faculty of Medicine and the evolutionary biologist Dr. Pierre-Marc Delaux from the Laboratoire de Recherche en Sciences Végétales (LRSV) in Toulouse/France, the team published their leads to the journal Current Biology.

When a root nodule bacterium encounters the roots of a leguminous plant in soil, the SYFO1 protein causes the small hairs of the root to change the direction of their-growth. They thus wrap themselves round the potential symbiotic partner. because of these bacterial helpers, legumes don’t need any nitrogenous fertilizer, in contrast to other plants. “If we understood precisely how the symbiosis comes into being, we could give crop plants back this special property they have lost in course of evolution,” says Ott. Both he and Grosse are members of the Cluster of Excellence CIBSS—Center for Integrative Biological Signaling Studies. Ott’s research at CIBSS involves studying the spatial organization of the signaling paths that enable the symbiotic relationship with symbiotic bacteria in first place. Grosse, on the opposite hand, focuses in his work in Freiburg on the cytoskeleton of animal cells. “In our collaboration, which was made possible by CIBSS, we were ready to contribute our expertise in several areas of specialization in absolute best way,” says Ott.

The team demonstrated in legume Medicago truncatula (barrel medic) that the root hairs of plants in which the gene for SYFO1 has been switched off are practically not capable of wrapping themselves round the bacteria. In further studies, the researchers discovered that the protein binds to actin, a component of the cytoskeleton, and at same time to the cell membrane outside the cells, thus changing the direction of its growth: rather than growing straight, the small hairs now change their direction and form a loop round the bacterium.

“SYFO1 constitutes a special innovative step in evolution of the plants,” explains Ott. “While formin proteins are present in many forms in cells and interact with actin, this special type only responds to symbiotic signals from the bacteria.”

The findings were reported in  Albert Ludwigs University of Freiburg