A copia-like retrotransposon Tgmr closely linked to the Rps1-k allele that confers race-specific resistance of soybean to Phytophthora sojae

We have isolated and characterized Tgmr, a copia-like retrotransposon, linked tightly to the Rpsl-k allele that confers race-specific resistance of soybean to the the fungal pathogen Phytophthora sojae. Southern analysis followed by PCR and sequence analyses, using primers based on sequences flanking the insertion site confirmed that the element was inserted in the neighboring region of Rpsl-k but not in that of the other four Rpsl alleles. This implies that Tgmr was transposed into the Rpsl-k flanking site after the divergence of Rpsl alleles. Southern analysis of a series of diverse soybean cultivars revealed a high level of polymorphism of Tgmr-related sequences. These results indicate that this low copy retroelement family could have been active in the soybean genome in the recent past. Tgmr contains long terminal repeats (LTR) and four non-overlapping open reading frames (ORF), presumably originating from mutations leading to stop codons of a single ORE The conserved domains for gag, protease, integrase, reverse transcriptase and RNaseH are present in the internal portion of the element. However, the protease, reverse transcriptase and RNaseH of this element are non-functional due to the presence of several stop codons. Possible transactivation of Tgmr and application of this element in insertional mutagenesis for soybean are discussed.