Amplification and transpositional activity of mPing in rice

Transposable elements are the most abundant type of DNAs in eukaryotic genomes. Thefirst active MITE, mPing has been activated by long-term tissue culture, anther culture, gamma-ray-irradiation. However, in this study, mPing was shown for the first time to be activated undernormal conditions in the rice cultivar Gimbozu and Nipponbare. In Gimbozu landraces withhigh-copy number of mPing, mPing was highly activated, generating ~50 new insertions pergeneration. This suggests that mPing is still accumulating its copies in these lines. In contrast,very low level of mPing activity was detected in one Gimbozu and Nipponbare strain for whichlow copy number of mPing is present. Comparison of de novo insertions with previouslyisolated new Gimbozu and older Nipponbare mPing elements implied that the negative selectionoccurred in stages: rapid elimination of insertions into exons and introns, and then slow andgradual removal of insertions near genes.