Functional characterization of differentially-expressed increased glyphosate resistance ( igrA ) gene in transgenic rice ( Oryza sativa L.)

Glyphosate is a very effective post-emergent herbicide which is widely used by farmers for controlling almost all kinds of annual and perennial weeds. Over the last thirty years, various strategies have been used to develop glyphosate-tolerant crop plants using the tolerant EPSPS alone and/or in combination with other glyphosate detoxifying genes. In this series, the bacterial igrA ( increased glyphosate resistance ) gene has also been reported to exhibit glyphosate tolerance by degrading into non-toxic products, although its efficacy was not inspected thoroughly. Considering the fact, we investigated the efficiency of igrA for glyphosate tolerance by overexpressing it into three different cellular locations viz, phloem (Ph) cytoplasm (Cy) or chloroplast (Ch) independently in transgenic rice plants. The igrA transgenic -plants were able to survive at the highest 50 µM glyphosate concentration while the wt died shortly even at 20 µM, confirmed by seed germination assay. Further, the transgenic plants showed improved tolerance upon foliar spraying with 2 mL/L (4.2 mM) of glyphosate in comparison to wt . All the three differentially expressed (Ph, Cy and Ch) transgenic rice lines exhibited almost similar responses towards glyphosate application. This study highlights the modest detoxification efficiency of igrA transgene irrespective of its differential cellular localization. The potential application of directed evolution strategies may improve the higher catalytic detoxification activity of igrA protein further, and could be successfully implemented for future development of higher glyphosate tolerant crops.