Regulation of the timing of transposable element excision during maize development.

The ability of transposable elements (TEs) to insert into or excise out of a genetic locus can be regulated by genetic, environmental, and developmental factors. Tissue- or organ-specific activity of TEs is a frequent and well-characterized example of spatial, developmental regulation. Regulation of the timing of TE activity during ontogeny is less well understood. To analyze timing, TE-induced variegation was quantified in the aleurone of maize kernels, a tissue composed of only a single layer of cells, and sector sizes were assigned to specific cell divisions in aleurone development. Three TE families, Mu, Spm, and Ac/Ds, were studied at two genetic loci. It was found that the frequency of transposon excision changes drastically (up to 30-fold increase or equivalent decrease) during the proliferation of the aleurone. Moreover, these changes occur at the same cell divisions in all three TE families. These results suggest that the timing of TE excision during maize development can be controlled by the host.