Root bacterial endophytes alter plant phenotype, but not physiology.

Jeremiah A Henning,Collin M Timm,Dale A Pelletier,Sara S Jawdy,Aimée T Classen,David J Weston

doi:10.7717/peerj.2606

Abstract

Plant traits, such as root and leaf area, influence how plants interact with their environment and the diverse microbiota living within plants can influence plant morphology and physiology. Here, we explored how three bacterial strains isolated from the Populus root microbiome, influenced plant phenotype. We chose three bacterial strains that differed in predicted metabolic capabilities, plant hormone production and metabolism, and secondary metabolite synthesis. We inoculated each bacterial strain on a single genotype of Populus trichocarpa and measured the response of plant growth related traits (root:shoot, biomass production, root and leaf growth rates) and physiological traits (chlorophyll content, net photosynthesis, net photosynthesis at saturating light–Asat, and saturating CO2–Amax). Overall, we found that bacterial root endophyte infection increased root growth rate up to 184% and leaf growth rate up to 137% relative to non-inoculated control plants, evidence that plants respond to bacteria by modifying morphology. However, endophyte inoculation had no influence on total plant biomass and photosynthetic traits (net photosynthesis, chlorophyll content). In sum, bacterial inoculation did not significantly increase plant carbon fixation and biomass, but their presence altered where and how carbon was being allocated in the plant host.

Highlights

A recent review exploring microbiome-mediated plant traits found that plant-associated microbes can modify 14 out of 30 commonly measured functional traits (Cornelissen et al, 2003; Friesen et al, 2011)
Bacterial strains differ in genomic content We compared the genomes of Burkholderia BT03 and Pseudomonas GM30 and GM41 based on predicted enzyme functions using the clusters of orthologous groups (COG) database (Table 1)
We found all three bacterial strains shared functions that were likely critical for establishment and survival in the plant microbiome including the production of the plant hormone auxin, pili, flagella, chemotaxis, increased signal transduction, and secretion systems

Summary

Introduction

A recent review exploring microbiome-mediated plant traits found that plant-associated microbes can modify 14 out of 30 commonly measured functional traits (Cornelissen et al, 2003; Friesen et al, 2011). This work demonstrated that plant growth promoting bacteria elicit numerous changes in host gene expression through multiple and simultaneous hormonal and immune response pathways (Verhagen et al, 2004; Walker et al, 2011; Weston et al, 2012; Drogue et al, 2014; Timm et al, 2016) These studies fall short in explaining how changes in gene expression influence the overall plant phenotype or plant function. Understanding the response of plant traits and overall plant phenotype to microbial strains remains a research gap

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Discussion

Conclusion