Myxobacterial Response to Methyljasmonate Exposure Indicates Contribution to Plant Recruitment of Micropredators

Abstract

Chemical exchanges between plants and microbes within rhizobiomes are critical to the development of community structure. Volatile root exudates such as the phytohormone methyljasmonate (MeJA) contribute to various plant stress responses and have been implicated to play a role in the maintenance of microbial communities. Myxobacteria are competent predators of plant pathogens and are generally considered beneficial to rhizobiomes. While plant recruitment of myxobacteria to stave off pathogens has been suggested, no involved chemical signaling processes are known. Herein we expose predatory myxobacteria to MeJA and employ untargeted mass spectrometry, motility assays, and RNA sequencing to monitor changes in features associated with predation such as specialized metabolism, swarm expansion, and production of lytic enzymes. From a panel of four myxobacteria, we observe the most robust metabolic response from plant-associated Archangium sp. strain Cb G35 with 10 μM MeJA impacting the production of at least 300 metabolites and inducing a ≥ fourfold change in transcription for 56 genes. We also observe that MeJA induces A. sp. motility supporting plant recruitment of a subset of the investigated micropredators. Provided the varying responses to MeJA exposure, our observations indicate that MeJA contributes to the recruitment of select predatory myxobacteria suggesting further efforts are required to explore the microbial impact of plant exudates associated with biotic stress.

Keywords: methyljasmonate; micropredator; myxobacteria; phytohormones; rhizobiome.

FIGURE 1

MeJA-impacted features provided by XCMS analysis of LC-MS/MS data after filtering feature tables for those with a ≥ fivefold change and p ≤ 0.05 with (A) depicting increased metabolites and (B) depicting decreased metabolites.

FIGURE 2

(A) Molecular network of MeJA and associated metabolites including nodes labeled with detected parent ions and edges labeled with cosine values. Predicted metabolites provided by NAP analysis of the GNPS-rendered cluster. *Multiple fatty acids and prenol lipids with identical exact masses predicted by NAP analysis. (B) Metabolites identified by GNPS analysis (cosine > 0.8) impacted by MeJA exposure.

FIGURE 3

Motility assays depicting cumulative change in swarm diameter post MeJA exposure. The symbol “^∗” indicates P < 0.05.

FIGURE 4

(A) Fold change data observed from A. sp. MeJA exposure experiments with increased transcription indicated with red and positive fold change values and decreased transcription indicated with blue and negative fold change values. Data represented for all genes with ≥ fourfold change (P < 0.05; n = 3 per condition). (B) General categories and classes associated with A. sp. genes with observed ≥ fourfold increases in transcription during MeJA exposure. (C) General categories associated with A. sp. genes with observed ≥ fourfold decreases in transcription during MeJA exposure.