Evolving insights to understanding mycorrhizas

Almost all land plant species form a symbiosis with mycorrhizal fungi. These soil fungi provide nutrients and other services to plants in return for plant carbohydrates. The recent application of microbial metagenomics, metatranscriptomics, and metabolomics to plants and their immediate surroundings confirms the key role of mycorrhizal fungi, rhizosphere bacteria and fungi, and suggests a world of hitherto undiscovered interactions (van der Heijden et al., this issue, pp. 1406–1423). This novel knowledge is leading to a paradigm-shifting view: plants cannot be considered as isolated individuals any more, but as metaorganisms, or holobionts (Hacquard & Schadt, this issue, pp. 1424– 1430) encompassing an active microbial community re-programming host physiology (see Pozo et al., this issue, pp. 1431–1436). This bears tremendous implications for plant ecophysiology and evolution, plant breeding, crop management and sustainable ecosystem management.