Soybean Transformation via the Pollen Tube Pathway

The pollen tube pathway method of transformation has been reported to be successful in several crops including soybean. DNA can be transferred by cutting the stigma following pollination and applying the DNA solution on the severed style. DNA presumably reaches the ovary by flowing down the pollen tube and then integrates into the just fertilized but undivided zygotic cells. To provide the molecular evidence for this procedure, the plasmids pBI221 carrying a CaMV35S promoter-beta glucuronidase (gus) gene-nos terminator gene fusion construct and pBI0122 carrying a CaMV35S promoter-bar-g73' terminator gene fusion construct were used. Approximately 5000 seeds were produced from the flowers treated with DNA. None of the seeds from the plants treated with DNA containing the bar gene were found to be as resistant as the positive control. Morphological variation was observed in some plants, but this was not observed in the following generation. Approximately 2% of the seeds from plants treated with DNA containing the gus gene had a positive reaction in the GUS assay, however, no GUS activity was observed in the plant leaves from those seeds. Less than 3% of progeny seeds tested expressed a positive reaction and polymerase chain reaction (PCR) with seedling DNA did not detect the gus gene. Thus, we were unable to confirm the positive results of others when we used screenable marker genes. INTRODUCTION Soybean transformation technology has been the subject of intense efforts over the past few years. Genetic transformation of soybean provides a method to improve economically important traits such as resistance to diseases, and pests, and tolerance to herbicides, and value-added traits, which are conferred by a single gene. Horsch et al. (1985) reported transformation and plant regeneration in tobacco. Thereafter, soybean transformation was reported independently by Hinchee et al. (1988) and McCabe et al. (1988) using Agrobacterium mediated DNA transfer