Signaling in the Rhizosphere

Abstract

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.

The ecological role of volatile mediated interactions belowground

“…A main role of those compounds is considered to be a defense as they are often used to fight off herbivory, pests and pathogens (Selvaraj 2015;Venturi & Keel 2016).…”

“…It is estimated that VOCs constitute about 1 % of plant secondary metabolites (Venturi & Keel 2016). The volatile blend released by plant roots consists of acids, aldehydes, alcohols, benzenoids, esters, ketones, terpenes, nitrogen and sulfur compounds as well as volatile phytohormones such as ethylene and methyl salicylate Dudareva et al 2013;Peñuelas et al 2014;Selvaraj 2015;.…”

“…It is estimated that VOCs constitute about 1 % of plant secondary metabolites (Venturi & Keel 2016). VOCs are small compounds of low molecular weight, lipophilic character, with high vapor pressure and low boiling points (Effmert et al 2012;Bitas et al 2013;Lemfack et al 2014;Schmidt et al 2015).…”

Range-expanding plant species and their belowground neighbours : digging into novel interactions

“…The majority of these interactions take place in the rhizosphere, which is the interface of plant roots and the surrounding soil (Philippot et al 2013). Here, plants exude volatile and non-volatile compounds, which in turn directly and indirectly attract soil organisms that together form the rhizosphere community (van Dam & Bouwmeester 2016;Venturi & Keel 2016;Schulz-Bohm et al 2017). As plant species vary in some of the chemical compounds they produce, they also attract and stimulate the growth of different soil organisms, thereby accumulating species-specific rhizosphere communities.…”

“…Over time, many plant species accumulate plant species-specific antagonistic and symbiotic-mutualistic soil organisms, thereby reducing or promoting themselves, while often having the opposite effect on neighbouring plant species . Plant species differentially shape soil communities (Bais et al 2006;Burns et al 2015), for example by producing different root exudates and volatiles (van Dam & Bouwmeester 2016;Venturi & Keel 2016). As phylogenetically closely related plant species are more likely to share such chemical traits than distantly related species (Gilbert & Parker 2016;Senior et al 2016), it may be expected that close relatives condition soil communities more similarly than distantly related species.…”