Temporal Changes in Transcripts of MITE Transposable Elements during Rice Endosperm Development

Repression of transposable elements (TEs) by DNA methylation is necessary for host plants to maintain genome integrity and prevent from harmful mutations. However, under certain circumstances, TEs are thought to escape from the host defense system and therefore activate their transcription. In A. thaliana and O. sativa, DNA demethylase targets to the sequence derived from TEs in the central cell, a progenitor cell of endosperm in the female gametophyte. This genome-wide DNA demethylation is also observed in the endosperm after fertilization. In this study, we survey transcripts generated from TEs during the rice endosperm development and some points of the embryo as a control using custom-made microarray. We found that TE transcripts are largely different in the embryo and endosperm. The expression patterns of TEs are dynamically up- and down-regulated during the endosperm development, especially for miniature inverted-repeat transposable elements (MITEs). Rice endosperm was harvested at 24 hr intervals from 2 to 7 days after pollination (DAP), and at 10 DAP. Rice embryo was dissected from the developing ovaries at 5, 7 and 10 DAP. These samples were used in this experiment.