Metabolic effects of glyphosate on transgenic maize expressing a G2-EPSPS gene from Pseudomonas fluorescens

Transgenic glyphosate-tolerant maize expressing 5-enolpyruvylshildmate-3-phosphate synthase (EPSPS) gene has been commercialized since 1996. However, it is not very clear how glyphosate treatment affects metabolite pathway in transgenic glyphosate-tolerant maize. Here, we obtained numerous of glyphosate-tolerant transgenic maize expressing a Pseudomonas fluoreseens G2-EPSPS gene. The expression and integration site of G2-EPSPS in transgenic main event Aro203, which can tolerate 3 folds of field usage of glyphosate, were investigated. Metabolite analysis was performed with Aro203 leaf samples using GC/MS method. The results showed that total 58 metabolites were identified. Over-expression of G2-EPSPS led to the increase of glutamate, malate, hydroxylamine and trehalose contents, but the decrease of glyoxylate, ribose and sucrose, compared to wild type plants. Twenty-two and 13 metabolites were up-regulated and down-regulated in nontransgenic maize by glyphosate treatments, respectively, whereas fewer metabolites (10 up-regulated and 4 down-regulated) were affected in transgenic maize. Glyphosate treatment significantly stimulated the accumulation of most amino acids but decreased lots of sugars in non-transgenic plants. The PCA analysis results showed that wild type plant cluster treated with glyphosate was clearly separated with other three clusters. The results in this study provide evidence to understand how genetic modification or glyphosate treatment affects the metabolite pathway in maize.