Jumping Genes: Leaping forward in functional characterization of soybeans with a transposable element.

The W4 locus in soybean encodes dihydroflavonol-4-reductase (DFR2) that regulates pigmentation patterns in flowers and hypocotyls. The w4-m allele has arisen through insertion of the Tgm9 transposon in the gene. In the mutable w4-m line, generation of purple flowers from white flowers indicates transposon’s excision, and its insertion into a second locus. We have used Tgm9 in isolating a male-sterility, female-sterility gene encoding a helicase. Sequencing revealed precise excision of the element from the helicase gene. Analysis of Tgm9-insertion sites among 142 independent Tgm9-induced mutants demonstrated that Tgm9 hops randomly to all 20 soybean chromosomes from its original location in DFR2 on chromosome 17. Although, transposition was random throughout the soybean genome, Tgm9 inserted more than once in 14 loci in the genome. Tgm9 appears to have a preference to jump into genes as observed for active transposable elements in other plant species. About 27% of the mutations induced by Tgm9 were in genes. Among the 116 unique mutants 22% contained insertions in exons or introns and are expected to cause complete loss of function. This study establishes the utility of this element for functional characterization of soybean genes