Detection of the starch modifying gbss-antisense construct in transgenic potatoes

Two potato varieties, Rustica and Desiree, were tested for a genetic modification consisting of a granule bound starch synthase (gbss) gene in antisense orientation combined with the endogenous B33 promoter and parts of the pBIN 19 plasmid vector including the neomycin phosphotransferase II (nptII) gene as a marker. Various polymerase chain reaction (PCR) primers were constructed for vector sequences, target inserts and the marker gene. At first no products with the predicted target-insert size were obtained. However, a long-template PCR combined with a nested PCR led to the expected amplification product in the Desiree variety. Results were confirmed by a restriction endonuclease digest, Southern blotting of fragments and by biochemical tests. The potato variety Rustica showed no target insert sequences on molecular analysis, nor did biochemical methods indicate modifications of the phenotype (i.e. reduced amounts of gbss protein and amylose). Only vector sequences and the marker gene were detected by the PCR method.