Exploring the use of transposon mobilization to produce a gene-tagged population for grapevine

Transposable elements (TEs), or transposons, are genetic elements that have the ability to mobilize within the genome of their host. They are known to influence gene function in many ways, and are believed to be key drivers of genomic evolution. We are interested in the TEs of grape for three main reasons. First, they provide a tool for clonal identification; second, they can be used to study the biology of TE function in very old clonal lineages; and, finally, TE mutagenesis provides a tool for gene tagging in grape. This paper focuses on this last role. More than 220,000 TE sequences are annotated in the grape reference sequence, with approximately 32,500 different types recognized, falling into 114 family groupings. It is estimated that between 40 and 50% of the grape genome is TE sequence. As these figures indicate, TEs are a highly diverse and very numerous element class within the grape genome. We are developing tissue-culture techniques to induce TE mobilization at the earliest possible time during somatic embryogenesis, in order to generate libraries of clones with unique insert sites. Somatic embryogenesis allows us to generate these populations with a common varietal background, simplifying both the genotyping and phenotyping of the resulting plants. We are also developing bioinformatic tools to detect and localize TEs within the grape genome. New TE sites are detected through the automated comparison of TE localization files between different somatic regenerants. To date, 1300 plants have been produced and planted into our experimental vineyard. Some vegetative mutant phenotypes are apparent, but it is too early to assess their fruiting characteristics.