In the last two decades, tremendous advances have been made in our understanding of the basic principles governing two agriculturally relevant symbioses of plants with beneficial microorganisms: i) the nitrogen-fixing nodule bacteria of legumes and angiosperms and ii) phosphate-acquiring mycorrhiza fungi. This special focus issue brings together articles covering aspects of evolution and phylogeny, diversity, signaling, differentiation, and development of new investigative tools. Together they provide a window into the exciting world of plant-microbe symbioses.
