Development of Ac and Ds transposon tagging lines for gene isolation in diploid potato

For the development of an efficient transposon tagging strategy it is impor tant to generate populations of plants containing unique independent transp oson insertions that will mutate genes of interest. To develop such a trans poson system in diploid potato the behavior of the autonomous maize transpo sable element Ac and the mobile Ds element was studied. A GBSS (Waxy) excis ion assay developed for Ac was used to monitor excision in somatic starch-f orming tissue like tubers and pollen. Excision of Ac results in production of amylose starch that stains blue with iodine. The frequency and patterns of blue staining starch granules on tuber slices enabled the identification of transformants with different Ac activity. After excision the GBSS compl ementation was usually not complete, probably due to the segment of DNA fla nking Ac that is left behind in the GBSS gene. Molecular and phenotypic ana lyses of 40 primary transformants classified into 4 phenotypic classes reve aled reproducible patterns. A very high percentage (32.5%) of the primary t ransformants clearly showed early excision in the first transformed cell as displayed both by the analysis of the GBSS excision marker gene as well as DNA blot analyses. Genotypes useful for tagging strategies were used for c rosses and the frequency of independent germinal transpositions was assesse d. In crosses to Ds genotypes, excision of Ds was revealed that correlated to the activity of the Ac genotype. A line displaying Ac amplification to m ultiple copies conferred a high frequency of independent Ds transpositions. The genotypes described here are useful in somatic insertion mutagenesis a imed at the isolation of tagged mutations in diploid potato.