Phenolic compound induction in plant-microbe and plant-insect interactions: a meta-analysis

Authors: Wallis, Christopher; GALAMEAU, ERIN - University Of California, Davis

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2020
Publication Date: 12/15/2020
Citation: Wallis, C.M., Galameau, E. 2020. Phenolic compound induction in plant-microbe and plant-insect interactions: a meta-analysis. Frontiers in Plant Science. 11:580753. https://doi.org/10.3389/fpls.2020.580753.
DOI: https://doi.org/10.3389/fpls.2020.580753

Interpretive Summary: Plant systemic defense pathways, including systemic acquired resistance (SAR) and induced systemic resistance (ISR), have been explored as a means of managing insect pests and pathogens. Previous studies observed that SAR and ISR may have negative feedback with one another that limit specific defenses of each, potentially complicating use in integrated pest management. However, these studies mostly focus on model hosts, a limited variety of inducers, and utilize different end defense markers, making broad-spectrum conclusions evasive. Therefore, a meta-analysis was conducted to summarize multiple studies that examined the ability of insect and microbial inducers to cause increases in systemic phenolic compound levels, a common SAR response. This meta-analysis concluded that pathogens, biological control agents, and chewing insects induced phenolic production, suggesting positive, not negative, cross-talk occurred between SAR and ISR pathways. These results therefore provide evidence that a re-evaluation is needed regarding theories of interplay between SAR and ISR. Future research should move beyond model systems, upon which most existing conclusions were formed, towards studies involving multiple hosts and defense inducers.

Technical Abstract: Plants have evolved at least two major defense pathways, systemic acquired resistance (SAR) and induced systemic resistance (ISR), to combat further attack following insect feeding or pathogen colonization. Each pathway is hypothesized to have different associated defenses, for example production of phenolic compounds for SAR. Likewise, each pathway is thought to be induced by different plant attackers, such as biotrophic pathogens and piercing-sucking insects for SAR. However, large-scale studies examining a variety of plant hosts and inducers have not been conducted to verify these hypotheses in full. Therefore, this study conducted a meta-analysis on results from studies that documented potential increases in systemic host phenolic levels, which are associated with SAR, in plants attacked by insects, infected by pathogens, or colonized by beneficial microbes. Meta-analyses observed overall significant phenolic induction following insect attack or microbial colonization. However, only bacteria and fungi colonization could be considered to consistently increase phenolic levels. Whereas chewing insects consistently caused greater host phenolic levels to occur, wood-boring and piercing-sucking insects did not. These results observed that plant hosts responded by having increased systemic phenolic levels to organisms, specifically chewing insects and beneficial microbes, not previously thought to cause SAR. Therefore, perceptions need to be adjusted about what organisms may trigger SAR, or, alternatively, what responses are considered specific for each defense pathway.