Exploiting an ancient signalling machinery to enjoy a nitrogen fixing symbiosis

For almost a century now it has been speculated that a transfer of the largely legume-specific symbiosis with nitrogen fixing rhizobium would be profitable in agriculture [1 and 2]. Up to now such a step has not been achieved, despite intensive research in this era. Novel insights in the underlying signalling networks leading to intracellular accommodation of rhizobium as well as mycorrhizal fungi of the Glomeromycota order show extensive commonalities between both interactions. As mycorrhizae symbiosis can be established basically with most higher plant species it raises questions why is it only in a few taxonomic lineages that the underlying signalling network could be hijacked by rhizobium. Unravelling this will lead to insights that are essential to achieve an old dream.

► Non-legume Parasponia provides insight in constraints of rhizobium symbiosis. ► Lipochito-oliogosaccharide signal molecules are not unique for rhizobium. ► Mycorrhizal fungi also produce lipochito-oliogosaccharide signals. ► Rhizobium has co-opted the mycorrhizal signalling network.