Role of physiological mechanisms and EPSPS gene expression in glyphosate resistance in wild soybeans (Glycine soja).

The physiological mechanisms underlying glyphosate resistance in wild soybean germplasm and relevant EPSPS gene expression were evaluated. These germplasms were selected by gradually increasing glyphosate selection pressure started from 2010. As indicated by a whole-plant dose response bioassay, ZYD-254 plants were resistant to glyphosate at concentrations of 1230gaeha(-1), but the susceptible plants (ZYD-16) were unable to survive in the presence of 300gaeha(-1) glyphosate. The ED50 values of resistant germplasm were approximately 8.8 times of the susceptible germplasm. Chlorophyll content was significantly decreased in ZYD-16 plants in comparison with ZYD-254 plants. ZYD-16 plants accumulated 10.1 times more shikimate in leaves at 5days after glyphosate treatment at 1230gaeha(-1) than ZYD-254 did. GST activity differed between ZYD-254 and ZYD-16 in three tissues. It was highest in leaves. There were no significant differences in EPSPS1 or EPSPS3 expression between two germplasms before exposure to glyphosate treatment. After glyphosate treatment, there was a 2- to 4-fold increase in EPSPS1 mRNA levels in ZYD-254, but there was no change in EPSPS3 mRNA levels in ZYD-254 or ZYD-16.