Plants need nitrogen to grow. Many legumes meet this need through a symbiotic relationship: they harbor bacteria that fix atmospheric nitrogen and make it available to the plant. Until now, it was largely unclear how a perennial plant regulates this symbiosis without destroying its bacterial partners. An international team led by TU Braunschweig, has now described a previously unknown mechanism: The black locust (Robinia pseudoacacia) employs a newly discovered family of small proteins that specifically “reprogram” its symbiotic bacteria for nitrogen fixation while keeping them alive. The findings are published in the prestigious journal “Science Advances.”