Soybean response to low glyphosate doses: Insights into the transcriptome, metabolic pathways and biomass production

Background:  Soybean cultivars show a positive response to low doses of glyphosate, called glyphosate hormesis, though the genetic and biochemical mechanisms are not fully understood.

Objective:  This study aimed to identify the pathways and differentially expressed genes (DEGs) related to glyphosate hormesis, along with their association with lignin and P content, and the shikimic acid pathway in glyphosate-resistant cultivars (RR and RR2) compared to a non-resistant cultivar (NR). It also evaluated how glyphosate hormesis impacted the electron transport rate (ETR) and biomass accumulation.

Results:  With 90% of reads matching the soybean reference genome, 31,515 genes were identified, including 587 DEGs. The DEGs enriched by glyphosate application in the NR cultivar were associated with flavone metabolism and auxin signaling, indicating impacts on phenylalanine-derived metabolites and developmental processes. In contrast, the RR cultivar showed enrichment in pathways related to stress response and fatty acid metabolism, while the RR2 cultivar exhibited enrichment in various metabolic pathways, notably lignin catabolism and auxin activity. Glyphosate treatments influenced electron transport rate (ETR), lignin, and P content, as well as components of the shikimic acid pathway and amino acid contents in soybean plants, with differential responses observed among cultivars and glyphosate doses. Overall, glyphosate hormesis led to increased dry biomass production across all cultivars.

Conclusion:  These findings provide insights into the molecular and physiological responses of soybean cultivars to glyphosate hormesis, highlighting the complex regulatory mechanisms that enable unique adaptations in each cultivar to the stress imposed by low herbicide doses.

Keywords:
Aromatic amino acids; Differentially expressed genes; Electron transport rate; Glycine max (L.) Merrill; GO enrichment; Lignin content; Shikimic acid pathway