TRANSFORMATION OF APPLE (MALUS DOMESTICA BORKH.) USING THE PHOSPHOMANNOSE ISOMERASE GENE AS A SELECTABLE MARKER

A positive selection system based on the use of the phosphomannose isomerase (pmi) gene as a selectable marker gene and mannose as the selective agent was used for the transformation of apple (Malus domestica Borkh.). pmi converts mannose-6-phosphate to fructose-6-phosphate. Only transformed cells are capable of utilizing mannose as a carbon source. Explant sensitivity to mannose was tested by transferring leaf explants on regeneration media supplemented with various combinations of mannose and sorbitol. Results indicated that apple is not able to utilize mannose as a carbon source. Young leaves of the apple cv. ‘Holsteiner Cox’ (Malus domestica Borkh.) were transformed via Agrobacterium tumefaciens. In order to develop and to optimize selection and transformation conditions, the histochemical marker gene for β-glucuronidase (GUS) was used to monitor transformation events. Transgenic plants regenerated on media containing various concentrations mannose and sorbitol. Integration of the phosphomannose isomerase gene was proven by PCR. The results indicated that the mannose selection system could be used for apple transformation, although selection conditions need to be optimised.