A 2-year field trial reveals no significant effects of GM high-methionine soybean on the rhizosphere bacterial communities

Insights into the effects of transgenic glyphosate-resistant semiwild soybean on soil microbial diversity

Transgenic soybean [Glycine max(L.) Merrill] currently covers approximately 80% of the global crop area for this species, with the majority of transgenic plants being glyphosate resistant (Roundup Ready, GR or RR). However, there is significant concern regarding the potential effects of GM crops and their byproducts on soil microbial communities. During our research, we discovered a type of semiwild soybean that emerged due to genetic drift at a transgenic test site. Nevertheless, the ecological risk to soil rhizosphere microorganisms associated with planting semiwild soybean following genetic drift remains unclear. Therefore, we conducted a field experiment and collected soil samples at various stages of plant growth. Our results indicate that the species diversity of rhizosphere bacteria in transgenic glyphosate-resistant semiwild soybean was also not significantly different from that observed in other types of soybean. Additionally, Basidiomycota had beneficial effects on rhizosphere fungi during the flowering and maturation stages in transgenic glyphosate-tolerant semiwild soybean. These findings provide valuable insights into how genetic drift in transgenic soybean may impact the soil microenvironment.

The response of microbiome assembly within different niches across four stages to the cultivation of glyphosate-tolerant and conventional soybean varieties

Introduction

Plants are inherently connected with the microbiome, which plays a crucial role in regulating various host plant biological processes, including immunity, nutrient acquisition, and resistance against abiotic and biotic stresses. Many factors affect the interaction between plants and microbiome.

Methods and results

In this study, microbiome samples were collected from five niches (bulk soil, rhizoplane, root endosphere, phylloplane, and leaf endosphere) across four developmental stages (seedling, flowering, podding, and maturity) of various soybean varieties. Composition and structure of bacterial and fungal communities were analyzed using 16S rRNA gene and ITS (Internally Transcribed Spacer) region amplicon sequencing. It was observed that both niches and developmental stages significantly impact on the assembly and composition of soybean microbiome. However, variety, presence of a transgene, and glyphosate application had minimal effects on microbial communities. The dominant microbiome varied across the five niches, with most containing beneficial microbial communities capable of promoting plant growth or increasing disease resistance. Types and abundance of the dominant microbes affected network stability, potentially resulting in functional changes in different ecological niches.

Conclusion

This study provides theoretical evidence for microbial protection of plants against diseases and demonstrates that systematic analysis of the composition and diversity of soybean microbiomes can contribute to the development of biological control technologies.

Impact of Insect-Resistant Transgenic Maize 2A-7 on Diversity and Dynamics of Bacterial Communities in Rhizosphere Soil

Artificial modification of Bacillus thuringiensis (Bt) proteins can effectively improve their resistance to target pests, but the effect of such modification on the diversity of rhizosphere microorganisms remains unclear. Transgenic maize 2A-7 contains two artificially modified Bt proteins, mCry1Ab and mCry2Ab. These proteins can enter soil and pose a potential threat to soil microbial diversity. To assess their impacts on rhizosphere bacteria communities, the contents of the two Bt proteins and changes in bacterial community diversity in the rhizosphere soils of transgenic maize 2A-7 and its control variety were analyzed at different growth stages in 2020. The results showed that the two Bt proteins were detected at low levels in the rhizosphere soils of 2A-7 plants. No significant differences in soil bacterial diversity were detected between 2A-7 and its control variety at any of the growth stages. Bioinformatics analysis indicated that the growth stage, rather than the cultivar, was the main factor causing changes in bacterial communities. This research provides valuable data for understanding the impact of Bt crops on the soil microbiome, and establishes a theoretical basis for evaluation of their safety.

Effects of Insect-Resistant Maize HGK60 on Community Diversity of Bacteria and Fungi in Rhizosphere Soil

The influence of biotech crops on microbial communities in rhizosphere soil is an important issue in biosafety assessments. The transgenic maize HGK60 harboring the Bt cry1Ah gene enhanced the resistance to lepidopteran pests, while the ecological risk of HGK60 maize on rhizosphere microorganisms is unclear. In this study, we comprehensively analyzed the diversity and composition of bacterial and fungal communities in the rhizosphere soil around Bt maize HGK60 and the near-isogenic non-Bt maize ZD958 at four growth stages via a high-throughput sequencing technique. The results showed that HGK60 maize unleashed temporary effects on the bacterial and fungal diversity and richness during the study plant's development, which would be restored after one cycle of plant cultivation due to the application of the same agricultural management. The differences of bacterial and fungal communities were marked by seasonality, while the different growth stage was the important factor as opposed to the cultivar contributing to the shifts in the bacterial and fungal communities' structure. This study will provide useful information regarding the impact of Bt transgenic maize on the soil microbiome and a theoretical basis for the development of a safety assessment approach for Bt maize in China.

The soybean rhizosphere: Metabolites, microbes, and beyond-A review

•

Rhizosphere microbial communities are important for plant health.

•

Specialized metabolites in the rhizosphere influence the microbial communities.

•

Isoflavones and saponins are major specialized metabolites secreted by soybean.

•

Secretion is regulated developmentally and nutritionally.

•

Possible links between specialized metabolites and microbial communities are highlighted.

The rhizosphere is the region close to a plant’s roots, where various interactions occur. Recent evidence indicates that plants influence rhizosphere microbial communities by secreting various metabolites and, in turn, the microbes influence the growth and health of the plants. Despite the importance of plant-derived metabolites in the rhizosphere, relatively little is known about their spatiotemporal distribution and dynamics. In addition to being an important crop, soybean (Glycine max) is a good model plant with which to study these rhizosphere interactions, because soybean plants have symbiotic relationships with rhizobia and arbuscular mycorrhizal fungi and secrete various specialized metabolites, such as isoflavones and saponins, into the soil. This review summarizes the characteristics of the soybean rhizosphere from the viewpoint of specialized metabolites and microbes and discusses future research perspectives. In sum, secretion of these metabolites is developmentally and nutritionally regulated and potentially alters the rhizosphere microbial communities.