Molecular Characterization of a Mutant Soybean Population Induced by an Endogenous Transposable Element, Tgm9

Madan K. Bhattacharyya, Iowa State University

Transposable elements, if land in a gene, the function of that gene could be lost leading to development of an altered phenotype. Such a mutant can then be used to clone the mutated gene. Alternatively if the mutant phenotype is desirable, the mutant gene can be introgressed into cultivars. We have identified and characterized the only known active endogenous transposable element, Tgm9, from soybean (Xu et al. 2010). We have shown that the element moves randomly throughout the soybean genome. Sequences of Tgm9-insertion sites among 98 mutants demonstrated that Tgm9 hopped from its original location in the DFR2 gene located in Chromosome 17 into 18 of the 20 soybean chromosomes. We also observed that although 98 insertions distributed almost randomly throughout 18 of the 20 chromosomes, seven of the 98 Tgm9 insertions were mapped to a single gene-rich region, located at the lower end of Chromosome 1. In this region, five of the seven Tgm9 insertions were mapped to genes. In other words, Tgm9 appears to have a preference to jump into genes as observed for active transposable elements in other plant species. We estimated that more than 1/3^rd of the time the element inserts into genes. Sequences carrying genes comprise less than 1/6^th of the soybean genome; therefore, this observation strongly suggests that Tgm9has a strong preference to hop into genes. This study thus establishes the utility of this element for creating mutations in soybean.