Construction of the one-time inducible transposon, COKC . The 5′ end was constructed in the third intron of the transposase gene, which was downstream of the PR-1a promoter. The 3′ end was constructed in the first intron of the selectable marker, modified epsps gene, involved in glyphosate resistance. Excision of COKC leads to a truncated transposase and marker genes and consequently a marker-off and defective COKC. t, transposase gene of Ac transposon (numbers indicate its corresponding 5 exons); e, modified rice epsps gene (numbers indicate its corresponding 8 exons). Restriction enzyme for Southern blot and primers for identifying excision events and expected PCR products are shown. The primer sets (CF, DR and JR) used to detect excision events are shown as a solid triangle. LB, left border; RB, right border; 5′ and 3′, Ac left and right-terminal inverted repeat; PR-1a, PR-1a inducible promoter; nos, nos promoter.