Plant Peptides Govern Terminal Differentiation of Bacteria in Symbiosis

<jats:title>Legume Symbiosome</jats:title> <jats:p> Leguminous plants (peas and beans) are major players in global nitrogen cycling by virtue of their symbioses with nitrogen-fixing bacteria that are harbored in specialized structures, called nodules, on the plant's roots. <jats:bold> Van de Velde <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1122" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184057">1122</jats:related-article> ) show that the host plant, <jats:italic>Medicago truncatula</jats:italic> produces nodule-specific cysteine-rich peptides, resembling natural plant defense peptides. The peptides enter the bacterial cells and promote its development into the mature symbiont. In a complementary study, <jats:bold> D. Wang <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1126" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184096">1126</jats:related-article> ), have identified the signal peptidase, also encoded by the plant, that is required for processing these specialized peptides into their active form. </jats:p>