In vitro gene expression and mRNA translocation from transformed walnut (Juglans regia) rootstocks expressing DsRED fluorescent protein to wild-type scions.

KEY MESSAGE: An in vitro grafting method was developed for examining gene translocation from rootstock to scion in walnut. Results showed the DsRED gene itself was not translocated but expressed mRNA was. Grafting is widely used in plants, especially in fruit and nut crops. Selected rootstocks can control scion growth and physiological traits, including shortening of the juvenile phase and controlling tree size. Rootstocks also can provide improved soil adaptation and pathogen resistance. Development of genetically modified (GM) fruit crops has progressed recently, but commercial cultivation is still limited due to the time required for evaluation and issues with deregulation. In this study, we evaluated the stability of DsRED marker gene expression in in vitro walnut shoots and examined translocation of the gene and its mRNA from transformed rootstock to wild-type scion. Results show that DsRED was expressed uniformly in transformed tissue-cultured shoots. When used as in vitro rootstocks, these had good graft affinity with wild-type control scion. PCR and qRT-PCR analysis showed that the DsRED gene was not transported from rootstock to scion, but the transcribed mRNA was translocated. This result provides further evidence of gene signal transport from rootstock to scion in fruit and nut crops.