Signaling in the Rhizosphere

Signaling studies in the rhizosphere have focused on close interactions between plants and symbiotic microorganisms. However, this focus is likely to expand to other microorganisms because the rhizomicrobiome is important for plant health and is able to influence the structure of the microbial community. We discuss here the shaping of the rhizomicrobiome and define which aspects can be considered signaling. We divide signaling in the rhizosphere into three categories: (i) between microbes, (ii) from plants to microorganisms, and (iii) from microorganisms to plants. Signals act on diverse organisms including the plant. Mycorrhizal and rhizobial interkingdom signaling has revealed its pivotal role in establishing associations, and the recent discovery of signaling with non-symbiotic microorganisms indicates the important role of communication in shaping the rhizomicrobiome.

TrendsThe plant and the rhizomicrobiome strongly influence each other via the secretion and detection of signaling compounds.Signaling between plants and rhizosphere microorganisms has been mainly studied in intimate symbiotic associations, in particular those involving mycorrhizal fungi and rhizobial bacteria; it is now evident that this is a more widespread phenomenon also involving non-symbiotic microorganisms.The rhizomicrobiome is a very rich and complex microbial community which undergoes intraspecies as well as interspecies signaling.Thus far, plant molecules including flavonoids, strigolactones, cutin momoners, and as yet unidentified low molecular weight compounds have been recognized as signals which are sensed by microorganisms.Microorganisms produce signals which affect plant growth and induce plant systemic resistance mainly via a process called priming.