Origin and activation mechanism of an active transposition of mPingin rice

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The distribution of miniature Ping (mPing) was studied in 50 wild Oryza accessions which encompassed 19 species representing nine genomes of genus Oryza. The mPing element was presented in all the accessions arid they were highly (more than 99%) similar each other. There are three major types of mPing elements; type 1 with 430bp originally found in Gimbozu (Osativa), type 2 with 430bp with 9bp base substitution al the position of 242-252, type 3 with 419bp with 11bp deletion at the position of 239-249. Type 2 and 3 are presented only in O.sativa and O.rugipogon, The wide presence of type 1 mping in all the other accession indicated mPing elements should be originated prior to the differentiation of the genus Oryza. Transposition and amplification of mPing and Ping are still underway in rice variety Gimbozu irrespective of its high copy number of mPing element (over 1000). In Gimbozu, more than 50 new transposition estimated to be occurred per plant per generation while no transposition activity of mPing was observed in Nippcnbare, To elucidate the genetic factors contributing to the transposition activity of mPing Gimbozu, F5 progeny lines of selfed F4 plants derived form the cross between Nipponbare and Gimbozu were used. The mPing transposition activity was evaluated from a number of new mPing insertions that were not presented in parental plants. Then, genetic map of Nipponbare x Gimbozu were constructed based on the insertion polymorphism of mPing (mPingSCAR marker) between two varieties. Results of a QTL analysis for the mPing activity revealed two major QTLs at chr 1 and chr4.