The use of transient GUS expression to develop an Agrobacterium-mediated gene transfer system for kiwifruit.

We have monitored transient GUS expression 4-5 days after cocultivation of leaf explants with Agrobacterium, in order to optimise parameters of cocultivation and so develop an efficient, reproducible gene transfer system in kiwifruit. Factors that were important included the health of the explant, the strain of Agrobacterium, and the binary vector used. Pre-culture of the leaf explants before cocultivation inhibited gene transfer at the cut edge. Placing the explants on moist filter paper during cocultivation gave increased frequencies of gene transfer. Stably transformed, kanamycin-resistant plants were obtained at good frequency from the optimised system. PCR and Southern analysis of the regenerated plants confirmed their transgenic nature.