Interplant Aboveground Signaling Prompts Upregulation of Auxin Promoter and Malate Transporter as Part of Defensive Response in the Neighboring Plants.

Connor Sweeney,Venkatachalam Lakshmanan,Harsh P Bais

doi:10.3389/fpls.2017.00595

Connor Sweeney, Venkatachalam Lakshmanan + Show 1 more

Open Access

https://doi.org/10.3389/fpls.2017.00595

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Abstract

When disrupted by stimuli such as herbivory, pathogenic infection, or mechanical wounding, plants secrete signals such as root exudates and volatile organic compounds (VOCs). The emission of VOCs induces a response in the neighboring plant communities and can improve plant fitness by alerting nearby plants of an impending threat and prompting them to alter their physiology for defensive purposes. In this study, we investigated the role of plant-derived signals, released as a result of mechanical wounding, that may play a role in intraspecific communication between Arabidopsis thaliana communities. Plant-derived signals released by the wounded plant resulted in more elaborate root development in the neighboring, unwounded plants. Such plant-derived signals also upregulated the Aluminum-activated malate transporter (ALMT1) responsible for the secretion of malic acid (MA) and the DR5 promoter, an auxin responsive promoter concentrated in root apex of the neighboring plants. We speculate that plant-derived signal-induced upregulation of root-specific ALMT1 in the undamaged neighboring plants sharing the environment with stressed plants may associate more with the benign microbes belowground. We also observed increased association of beneficial bacterium Bacillus subtilis UD1022 on roots of the neighboring plants sharing environment with the damaged plants. Wounding-induced plant-derived signals therefore induce defense mechanisms in the undamaged, local plants, eliciting a two-pronged preemptive response of more rapid root growth and up-regulation of ALMT1, resulting in increased association with beneficial microbiome.

Highlights

Studies have shown that aboveground pathogen and herbivore attack shifts microbiome activity at the belowground level (Yang et al, 2011; Song et al, 2016)
Mechanical wounding of A. thaliana plant facilitated the release of airborne volatile organic compounds (VOCs) that induced an elaborate series of defensemechanisms in the neighboring seedlings
We speculated that the no other signals besides VOCs could be exchanged in the partition plates, VOCs may play a critical role in signaling between injured donors and recipient communities

Summary

Introduction

Studies have shown that aboveground pathogen and herbivore attack shifts microbiome activity at the belowground level (Yang et al, 2011; Song et al, 2016). We have shown previously that plants under attack by pathogenic bacteria induce a shoot-to-root systemic signal, inducing roots to recruit benign, protective microbes (Rudrappa et al, 2008; Lakshmanan et al, 2012). When colonized on plant roots, B. subtilis forms a sort of protective armor around its host by secreting antimicrobial compounds, namely the lipopeptide surfactin, that inhibit the growth of fungi, nematodes, and pathogenic bacteria like Pseudomonas syringae (Vlamakis et al, 2013). In addition to root-exuded chemicals, plants are known to signal other plants, microbes, nematodes, and insects via emission of non-polar volatile organic compounds (VOCs) (Delory et al, 2016). It is known that plant-derived chemical compounds impact plants response against microbes and mediate changes in plant development via upregulation of growth regulator response (Dudareva et al, 2013)

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