Does Wheat Genetically Modified for Disease Resistance Affect Root-Colonizing Pseudomonads and Arbuscular Mycorrhizal Fungi?

Abstract

This study aimed to evaluate the impact of genetically modified (GM) wheat with introduced pm3b mildew resistance transgene, on two types of root-colonizing microorganisms, namely pseudomonads and arbuscular mycorrhizal fungi (AMF). Our investigations were carried out in field trials over three field seasons and at two locations. Serial dilution in selective King's B medium and microscopy were used to assess the abundance of cultivable pseudomonads and AMF, respectively. We developed a denaturing gradient gel electrophoresis (DGGE) method to characterize the diversity of the pqqC gene, which is involved in Pseudomonas phosphate solubilization. A major result was that in the first field season Pseudomonas abundances and diversity on roots of GM pm3b lines, but also on non-GM sister lines were different from those of the parental lines and conventional wheat cultivars. This indicates a strong effect of the procedures by which these plants were created, as GM and sister lines were generated via tissue cultures and propagated in the greenhouse. Moreover, Pseudomonas population sizes and DGGE profiles varied considerably between individual GM lines with different genomic locations of the pm3b transgene. At individual time points, differences in Pseudomonas and AMF accumulation between GM and control lines were detected, but they were not consistent and much less pronounced than differences detected between young and old plants, different conventional wheat cultivars or at different locations and field seasons. Thus, we conclude that impacts of GM wheat on plant-beneficial root-colonizing microorganisms are minor and not of ecological importance. The cultivation-independent pqqC-DGGE approach proved to be a useful tool for monitoring the dynamics of Pseudomonas populations in a wheat field and even sensitive enough for detecting population responses to altered plant physiology.

Persistence of seeds, seedlings and plants, performance of transgenic wheat in weed communities in the field and effects on fallow weed diversity

“…In our case, however, the wheat plants carrying Pm3b and Chi and Glu transgenes did not seem to change the post-harvest vegetation, at least within the 6-month time period. Our findings correspond to the results of several companion studies which showed no effects of these particular GM plants on non-target organisms, such as insect species (Alvarez-Alfageme et al, 2011;Peter et al, 2010;von Burg et al, 2010), soil fauna (Duc et al, 2011) or soil beneficial bacteria and mycorrhizal fungi (Meyer et al, 2013;Song Wilson et al, 2010).…”

Belowground environmental effects of transgenic crops: a soil microbial perspective

“…Differences in AMF root colonisation and Pseudomonas population dynamics were observed among wheat plants expressing the pm3b mildew resistance transgene and parental lines. Conversely, no differences were detected between GM and non-GM sister lines, obtained through the same tissue culture and regeneration process, demonstrating that the differences in root colonisation may be ascribed to the transformation technology [51].…”

The plant microbiome

“…Other studies have not found any significant differences in rhizosphere microbiomes between wild-type maize and maize genetically engineered to produce Bacillus thuringiensis (Bt) toxin [100,101], although this may be due to Bt toxin being insecticidal rather than antibacterial. Also, in the wheat rhizosphere, introduction of the pm3b gene conferring resistance to mildew had minimal effect on pseudomonads and mycorrhizal fungi populations [102]. Disease resistance, including production of antimicrobial compounds, is a trait likely to be introduced as a result of molecular breeding or genetic modification in attempts to control diseases.…”