Small molecules below‐ground: the role of specialized metabolites in the rhizosphere

Abstract

Soil communities are diverse taxonomically and functionally. This ecosystem experiences highly complex networks of interactions, but may also present functionally independent entities. Plant roots, a metabolically active hotspot in the soil, take an essential part in below-ground interactions. While plants are known to release an extremely high portion of the fixated carbon to the soil, less information is known about the composition and role of C-containing compounds in the rhizosphere, in particular those involved in chemical communication. Specialized metabolites (or secondary metabolites) produced by plants and their associated microbes have a critical role in various biological activities that modulate the behavior of neighboring organisms. Thus, elucidating the chemical composition and function of specialized metabolites in the rhizosphere is a key element in understanding interactions in this below-ground environment. Here, we review key classes of specialized metabolites that occur as mostly non-volatile compounds in root exudates or are emitted as volatile organic compounds (VOCs). The role of these metabolites in below-ground interactions and response to nutrient deficiency, as well as their tissue and cell type-specific biosynthesis and release are discussed in detail.

Aboveground herbivory induced jasmonates disproportionately reduce plant reproductive potential by facilitating root nematode infestation

“…An alternative explanation might be that herbivory changes plant attractiveness by influencing, for instance, root exudation or root volatile emission patterns. Nematodes exploit systemically induced root volatiles for host location (Ali, Alborn, & Stelinski, 2011;Kihika, Murungi, & Coyne, 2017;Massalha, Korenblum, Tholl, & Aharoni, 2017). Further studies might aim at investigating the relative contribution of these effects to herbivory induced facilitation of nematode infestation.…”

Rhizosphere modelling reveals spatiotemporal distribution of daidzein shaping soybean rhizosphere bacterial community

“…The rhizosphere, defined as the zone of soil surrounding the root that is affected by it (Hartmann, Rothballer, & Schmid, ; Hiltner, ), is pivotal in both nutrient uptake and interactions with a diverse range of soil microbes (Bakker, Pieterse, de Jonge, & Berendsen, ). Previous studies provided evidence that plant metabolites secreted from roots provoke changes in rhizosphere microbial communities and mediate plant–microbe interactions, from symbiotic to commensal to pathogenic, suggesting the importance of plant metabolites in the rhizosphere for promoting the growth and health of plants (Berendsen, Pieterse, & Bakker, ; Massalha, Korenblum, Tholl, & Aharoni, ; Sasse, Martinoia, & Northen, ). Despite the importance of root‐secreted metabolites, little is known of the distribution and fate of these molecules in the rhizosphere (Sugiyama, ).…”

“…Plant specialized metabolites have important ecological functions in the rhizosphere, such as acting as signals for symbiosis, repelling enemies, and modifying microbial communities (Chen et al, 2019;Huang et al, 2019;Massalha, 2017). Volatile compounds are thought to facilitate communication over larger distances (Rasmann et al, 2005;Schulz-Bohm et al, 2018), whereas nonvolatile compounds such as coumarins (Stringlis et al, 2018) and flavonoids appear to exert their influences near plant roots.…”

Linking soil's volatilome to microbes and plant roots highlights the importance of microbes as emitters of belowground volatile signals

“…Volatile organic compounds, small molecules with a low boiling point and high vapour pressure, are indeed another important group of chemical signals exchanged between plants and microbes. Because of their volatile nature, volatile organic compounds can diffuse in the soil and convey messages many centimetres away from their emitters (Rasmann et al, 2005;Wenke et al, 2010;Peñuelas et al, 2014;Massalha et al, 2017;Schulz-Bohm et al, 2018;Sharifi and Ryu, 2018). To date, 841 volatiles that might act as signals to plants have been documented from soil associated microbes, even though a much higher number might exist (Schenkel et al, 2015).…”