The rice retrotransposon Tos17 prefers low-copy-number sequences as integration targets

The rice retrotransposon Tos17 is highly activated by tissue culture. To ev aluate the impact of transposition of Tos17 on the rice genome and examine its utility for insertional mutagenesis, more than 100 sequences flanking n ewly transposed Tos17 copies were characterised. The 5-bp target-site dupli cations flanking Tos17 did not show any consensus sequence, and preferred n ucleotides, A/T and G/C, were only found at the second and third nucleotide s from both ends of the target site duplications, respectively, indicating that Tos17 has relatively low target-site specificity at the nucleotide seq uence level. Integration targets were widely distributed over the chromosom es; however, preferential integration into the sucrose synthase 2 gene and into Tos17 itself was demonstrated by PCR screening using pooled DNA prepar ed from the mutant population. Hybridisation studies indicated that Tos17 p referentially integrates into low-copy-number regions of the genome. In agr eement with this result, about 30% of flanking sequences examined showed si gnificant homology to known genes. Taken together, these results show that Tos17 can have a significant impact on the rice genome and can be used as a tool for efficient insertional mutagenesis.