Root-emitted volatile organic compounds: can they mediate belowground plant-plant interactions?

Abstract

Background Aboveground, plants release volatile organic compounds (VOCs) that act as chemical signals between neighbouring plants. It is now well documented that VOCs emitted by the roots in the plant rhizosphere also play important ecological roles in the soil ecosystem, notably in plant defence because they are involved in interactions between plants, phytophagous pests and organisms of the third trophic level. The roles played by root-emitted VOCs in between-and withinplant signalling, however, are still poorly documented in the scientific literature. Scope Given that (1) plants release volatile cues mediating plant-plant interactions aboveground, (2) roots can detect the chemical signals originating from their neighbours, and (3) roots release VOCs involved in biotic interactions belowground, the aim of this paper is to discuss the roles of VOCs in between-and withinplant signalling belowground. We also highlight the technical challenges associated with the analysis of root-emitted VOCs and the design of experiments targeting volatile-mediated root-root interactions. Conclusions We conclude that root-root interactions mediated by volatile cues deserve more research attention and that both the analytical tools and methods developed to study the ecological roles played by VOCs in interplant signalling aboveground can be adapted to focus on the roles played by root-emitted VOCs in between-and within-plant signalling.

Volatile terpenoids: multiple functions, biosynthesis, modulation and manipulation by genetic engineering

“…Terpenoids are also involved in the plant-plant interaction, repelling pests and attracting enemies of pests (Unsicker et al 2009). Volatile terpenoids are involved especially in attracting pollinators, seed dispersal, defense against herbivores from both below-and above-ground (Ali et al 2012;Delory et al 2016), plant-plant signaling and protection against pathogens (Huang et al 2012) (Fig. 2).…”

“…Arabidopsis has been shown to emit two terpenoids, (3,S)-(E)-nerolidol and its derivative (E)-4,8-dimethyl-1,3,7-nonatriene, when the strawberry nerolidol synthase gene was introduced into the plants, resulting in greater attraction of the predators of predatory mites (Kappers et al 2005). Caryophyllene, emitted from the roots of Maize plants, is known to be an herbivore-induced below-ground signal, which strongly attracts entomopathogenic nematodes (Rasmann et al 2005;Delory et al 2016). Similarly, Ozawa et al (2000) demonstrated that (Lotus japonicus) shoots infested with spider mites released a blend of volatiles that attracted predators of mites (Phytoseiulus persimilis).…”

“…The repellent/attraction properties of various terpenoid volatiles in petunia flower were observed via silencing the biosynthetic genes individually responsible for the production of scent compounds (Kessler et al 2013). Another example of floral scent engineering is the introduction of a maize sesquiterpene synthase gene (TPS10) into Arabidopsis, leading to the production of a significant amount of various sesquiterpenes that are exploited by the female parasitoid wasp C. marginiventris to navigate to their potential lepidopteran host (Schnee et al 2006;Delory et al 2016). Manipulation of genetic engineering for sesquiterpenes production seems a challenging task and is less successful compared with that for monoterpenes due to lack of suitable precursors.…”

“…Furthermore, herbivore-induced monoterpenoids act as airborne signals to nearby plants in response to insect attack such as (E)-β-ocimene (Arimura et al 2004). Although terpenes are mostly studied in the above-ground tissues, recently, their novel function in the below-ground environment, as signaling molecules, has been identified (Karban et al 2014;Delory et al 2016). For example, β-caryophyllene, released from the roots of maize plants against beetle (Diabrotica virgifera) attack, acts as a volatile signal to attract predatory nematodes, which will defend plants indirectly from further damage (Rasmann et al 2005).…”

Rapid mineralization of biogenic volatile organic compounds in temperate and Arctic soils

“…In addition to the uptake from the atmosphere, the very fast mineralization rates are likely important in shaping the net 340 BVOC emissions from soil. The net BVOC release from soil to the atmosphere in general is low compared to the plant emissions (Peñuelas et al, 2014), but emissions may represent a minor portion of the amount that was excreted by soil microbes (Insam and Seewald, 2010;Garbeva et al, 2014) or by roots (Lin et al, 2007;Delory et al, 2016), produced for example with the purpose of communication. It is thus possible that BVOCs are a significant source of carbon to soil microbes and hence that BVOC formation and degradation may be an important but little recognized part of internal 345 carbon cycling in soil.…”