The Chemistry of Stress: Understanding the ‘Cry for Help’ of Plant Roots

Abstract

Plants are faced with various biotic and abiotic stresses during their life cycle. To withstand these stresses, plants have evolved adaptive strategies including the production of a wide array of primary and secondary metabolites. Some of these metabolites can have direct defensive effects, while others act as chemical cues attracting beneficial (micro)organisms for protection. Similar to aboveground plant tissues, plant roots also appear to have evolved “a cry for help” response upon exposure to stress, leading to the recruitment of beneficial microorganisms to help minimize the damage caused by the stress. Furthermore, emerging evidence indicates that microbial recruitment to the plant roots is, at least in part, mediated by quantitative and/or qualitative changes in root exudate composition. Both volatile and water-soluble compounds have been implicated as important signals for the recruitment and activation of beneficial root-associated microbes. Here we provide an overview of our current understanding of belowground chemical communication, particularly how stressed plants shape its protective root microbiome.

Extended Plant Metarhizobiome: Understanding Volatile Organic Compound Signaling in Plant-Microbe Metapopulation Networks

“…For example, in response to VOCs produced by the fungal pathogen Fusarium culmorum , the bacterium Serratia plymuthica has been shown to upregulate the production of sodorifen VOC ( 51 ), which induced the expression of plant defense-related genes in Arabidopsis thaliana ( 64 ). It is thus plausible that microbes are the first to sense the stress and produce specific metabolites to alert their host plant, as has also been suggested by Rizaludin et al ( 65 ). VOC-sensing bacteria could thus warn plants about invading pathogens earlier by allowing activation of immune responses (VOC priming effect) in response to VOCs emitted by distant microbial communities ( 66 ), as has also been reported for aboveground VOC-mediated plant-to-plant warning against insect and disease attack ( 20 ).…”

Biosynthesis, evolution and ecology of microbial terpenoids

“…for the protection of plants against biotic and abiotic stresses. 265 There are still many unknowns on the real terpenoid producer(s) in many cases of plant–microbe interactions and on how plants and insects can benefit from the terpenoids produced by host-associated microbes. Furthermore, many terpenoids have been reported from marine invertebrates such as sponges or octocorals, where they act as a predator deterrents, antifouling or space-competition agents 10,266 and it remains to be clarified whether they are produced by hosts and/or associated microorganisms.…”

Probiotic Endophytes for More Sustainable Banana Production

“…Beyond the cultivar, geographic location, and fertilization management, it is consistent that a shift of banana endospheric microbial communities structure is consistently observed [ 80 , 89 ]. However, to understand the “cry for help” mechanism and keystone candidates relationship, we must combine biological and chemical approaches [ 111 ], especially when designing SynComs that promote resilience to all types of stresses. Despite the progress made, we still need to know if the observed changes of γ-Proteobacteria abundance in Fusarium -infected plants occur in other diseases such as black Sigatoka.…”