The endogenous transposable element Tgm9 is suitable for generating knockout mutants for functional analyses of soybean genes and genetic improvement in soybean

In soybean, variegated flowers can be caused by somatic excision of the CACTA-type transposable element Tgm9 from Intron 2 of the DFR2 gene encoding dihydroflavonol-4-reductase of the anthocyanin pigment biosynthetic pathway. DFR2 was mapped to the W4 locus, where the allele containing Tgm9 was termed w4-m. In this study we have demonstrated that previously identified morphological mutants (three chlorophyll deficient mutants, one male sterile-female fertile mutant, and three partial female sterile mutants) were caused by insertion of Tgm9 following its excision from DFR2. Analyses of Tgm9 insertion sites among 105 independent mutants demonstrated that Tgm9 hops to all 20 soybean chromosomes from its original location on Chromosome 17. Some genomic regions are prone to increased Tgm9-insertions. Tgm9 transposed over 25% of the time into exon or intron sequences. Tgm9 is therefore suitable for generating an indexed insertional mutant collection for functional analyses of most soybean genes. Furthermore, desirable Tgm9-induced stable knockout mutants can be utilized in generating improved traits for commercial soybean cultivars.