Grafting Imparts Glyphosate Resistance in Soybean

Grafting is a widely-adopted cultural method to incorporate desired traits of rootstock with those of the scion and has been used successfully to address many biotic and abiotic stresses, including drought/waterlogging, insects, and diseases. However, it is not known if a herbicide resistance trait can be transferred across a graft union. Using Roundup Ready (RR; glyphosate-resistant) soybean grafted with conventional (CM; nontransgenic and glyphosate-sensitive) soybean, we show that grafting is capable of transferring glyphosate resistance from RR rootstocks to CM scions. Grafts of CN/CN (scion/rootstock), CN/RR, RR/CN, and RR/RR were treated with potassium salt of glyphosate at 0.28, 0.84 and 1.68 kg ae ha(-1). The CN/RR plants survived glyphosate treatment at 0.84 and 1.68 kg ha(-1) while CN/CN plants were killed, indicating that glyphosate resistance is systemically mobile across the graft union. Intraspecies transfer of glyphosate resistance was unidirectional from root to shoot, since RR/CN plants were killed by glyphosate. The glyphosate resistance trait is conferred by CP4 5-enolpyruvylshikimate-3-phosphate synthase (CP4-EPSPS); therefore, we further examined whether CP4-EPSPS played a role in the phenomenon. CP4-EPSPS was detected in the CM scion of CN/RR plants by enzyme-linked immunosorbent assay (ELISA) but only 0.001% of that detected in RR leaf. This concentration is unlikely to have contributed significantly to the glyphosate resistance observed in CN/RR plants. Amino acid systemic trafficking and/or tissue specific glyphosate resistance are more likely the reasons for this phenomenon. These results show that grafting a transgenic herbicide-resistant rootstock to a nonresistant scion can confer resistance to the entire plant.