Symbiosis and the social network of higher plants

► Most plants associate with arbuscular mycorrhizal fungi using an ancient and highly conserved SYM pathway. ► Most of this pathway has been lost in some plant families including the Brassicaceae. ► This SYM pathway has been usurped by some plant families such as the legumes to instead also associate with nitrogen-fixing bacteria. ► The possibility of manipulating this SYM pathway to engineer more efficient associations between nonleguminous crops and nitrogen-fixing bacteria is discussed.