Ancestral alliances: Plant mutualistic symbioses with fungi and bacteria

Abstract

BACKGROUND: Among the extensive cortège of plant-Associated microorganisms (the socalled plant microbiota), mutualistic fungal and bacterial symbionts are striking examples of soil microorganisms that have successfully coevolved with their hosts since plants adapted to terrestrial ecosystems.They promote plant growth by facilitating the acquisition of scarce nutrients.In these associations, plant root colonization requires complexmolecular cross-Talk between symbiotic partners to activate a variety of host developmental pathways and specialized symbiotic tissues and organs.Despite the evolutionary distances that separate mycorrhizal and nitrogen-fixing symbioses, recent research has identified certain highly conserved features associated with early stages of root colonization.We focus on recent and emerging areas of investigation concerning thesemajormutualistic symbioses and discuss some of the molecular pathways and cellular mechanisms involved in their evolution and development.