Mechanism of Genome Adaptive Response to Glyphosate Challenge in Amaranthus tuberculatus

Glyphosate is a non-selective, most widely used herbicide world-wide, especially upon commercialization of glyphosate-resistant crops. As a result of extensive and exclusive use of glyphosate, many agricultural weeds have evolved resistance to this herbicide. The molecular target of glyphosate, 5-enopyruvlyshikimate-3-phosphate synthase (EPSPS) gene amplification, conferring resistance to this herbicides is a novel mechanisms and was first documented in glyphosate-resistant Amaranthus palmeri, and later in many others economically important and troublesome weeds, including A. tuberculatus. However, information about the mechanisms and cytogenetic consequences associated with EPSPS gene amplification is elusive. Use of advanced molecular cytogenetic techniques enable understanding of genome response to glyphosate selection resulting in EPSPS gene amplification. Results of florescent in situ hybridization (FISH) analysis indicate that the native locus of EPSPS gene is located on homologous chromosomes, at pericentromeric region of A. tuberculatus. Further characterization of A. tuberculatus, with varying EPSPS copies demonstrate that the initial EPSPS gene duplication may have occurred as a result of unequal crossovers, and that the subsequent multiplication of the loci may can occur as a result of other chromosomal aberrations. Overall, unequal recombination may prompt change in EPSPS copy number and also a prerequisite for further EPSPS gene amplification in A. tuberculatus.