Efficient retrieval of recombinant sequences of GM plants by Cauliflower Mosaic Virus 35S promoter-based bidirectional LT-RADE

Identification of genetically modified (GM) plants remains a difficult task, especially when few information on the GM content in a sample is available. The CaMV P-35S is a commonly applied genetic element in GM plants and represents as such a suitable starting point for the tracing of GM plants. Here, the application of a CaMV P-35S LT-RADE genome walking method on five different GM crops is documented: MON810 maize, LLRICE62 rice, T45 rapeseed, A2704-12 soybean and LLCOTTON25 cotton. Two sets of oligonucleotide primers are presented as a potential forward and reverse genome walking strategy with genomic DNA as template. The method’s applicability for assessing the recombinant nature of P-35S positive signals is discussed in detail. This study demonstrates the general use of LT-RADE in molecular characterization of GMOs retrieving several previously unknown transgenic insert nucleotide sequences. Current limitations and future developments are discussed.