Transgenic banana plants expressing Xanthomonas wilt resistance genes revealed a stable non-target bacterial colonization structure.

Jean Nimusiima,Martina Köberl,Jerome Kubiriba,John Baptist Tumuhairwe,Charles Staver,Gabriele Berg

doi:10.1038/srep18078

Abstract

Africa is among the continents where the battle over genetically modified crops is currently being played out. The impact of GM in Africa could potentially be very positive. In Uganda, researchers have developed transgenic banana lines resistant to banana Xanthomonas wilt. The transgenic lines expressing hrap and pflp can provide a timely solution to the pandemic. However, the impact of the transgenes expression on non-target microorganisms has not yet been investigated. To study this effect, transgenic and control lines were grown under field conditions and their associated microbiome was investigated by 16S rRNA gene profiling combining amplicon sequencing and molecular fingerprinting. Three years after sucker planting, no statistically significant differences between transgenic lines and their non-modified predecessors were detected for their associated bacterial communities. The overall gammaproteobacterial rhizosphere microbiome was highly dominated by Xanthomonadales, while Pseudomonadales and Enterobacteriales were accumulated in the pseudostem. Shannon indices revealed much higher diversity in the rhizosphere than in the pseudostem endosphere. However, the expression of the transgenes did not result in changes in the diversity of Gammaproteobacteria, the closest relatives of the target pathogen. In this field experiment, the expression of the resistance genes appears to have no consequences for non-target rhizobacteria and endophytes.

Highlights

Hypersensitive response (HR) in plants challenged with Gram-negative pathogens
In our risk assessment study for transgenic banana lines resistant to banana Xanthomonas wilt (BXW), we investigated two microenvironments and found statistically significant differences for the composition and diversity of rhizosphere and endosphere bacterial communities
Three years after sucker planting, we found no differences between transgenic lines and their non-modified predecessors, indicating that in our field experiment the insertion of the Banana Xanthomonas wilt (BXW) resistance genes in the banana genome appears to have no consequences for non-target rhizobacteria and endophytes of healthy banana plants

Summary

Introduction

Hypersensitive response (HR) in plants challenged with Gram-negative pathogens. Hrap intensifies the HR activation by dissociating harpin multimers into dimers and monomers which triggers a stronger hypersensitive cell death (HCD) necrosis leading to a systemic acquired resistance (SAR) of the plant[9,10]. To move beyond the 30 years debates on existing GM crops, where they are often discussed in “black and white”, we need a bigger picture which is “nuanced, equivocal and undeniably messy”, a data-driven debate as well as risk assessment studies for GM crops for Africa[17]. In this respect, we analyzed the plant-associated microbiome of transgenic banana lines expressing sweet pepper hrap and pflp genes in comparison to their not genetically modified predecessors grown under natural soil conditions in a confined field trial in Uganda. We monitored the effect of the transgenes on the composition and diversity of the banana-associated microbiome in the rhizosphere and the pseudostem endosphere, with special focus on the gammaproteobacterial community which comprises the causal agent of BXW

Methods

Results

Conclusion