Abstract
Two different selection systems which do not require the use of antibiotics or herbicides were tested in apple transformation: the mannose/phosphomannose isomerase (pmi) and the galactose/UDP-glucose:galactose-1-phosphate uridyl-transferase (galT) system. Pmi transgenic plants are capable of converting the non-metabolisable sugar mannose into a usable source of carbon, fructose. The toxicity of galactose is attributed to accumulation of galactose-1-phosphate. GalT converts galactose-1-phosphate to UDP-galactose and glucose-1-phosphate, that might be sufficient to provide a reduction of galactose toxicity suitable to allow transgenic plants to survive on galactose media. Sensitivity of apple to the selective agents mannose and galactose was tested by exposing leaf explants to various combinations of mannose and sorbitol or galactose and sorbitol supplemented media. Results indicated that apple is not able to utilize these sugars as a carbon source. Young leaves of Malus domestica Borkh. 'Holsteiner Cox' were transformed via Agrobacterium tumefaciens with the binary vectors pNOV2819-GUS (pmi and GUS gene) or pBI-galT (galT, nptll and GUS gene) and selected using mannose, galactose or kanamycin. Several transgenic lines were regenerated using the pmi/mannose system. Transgene integration was confirmed by PCR and southern blot analysis. Explants transformed with pBI-galT developed only callus when galactose was used as selective agent. Thus no transgenic plants were recovered using the galT/galactose selection system.
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