UV-B radiation induces Mu element somatic transposition in maize

Abstract

The maize Mutator (MuDR/Mu) transposon family is the most active DNA transposon inplants (Lisch 2002). The Mu family contains diverse elements, all sharing similar ~215 bpterminal inverted repeats (TIRs). MuDR is the autonomous element, and a transcriptionallyactive MuDR is required for transposition of the non-autonomous Mu elements (Chomet et al.,1991). MuDR contains two genes, mudrA and mudrB (Figure 1A); mudrA encodes the MURAtransposase, and mudrB encodes a protein with unknown function. To avoid the deleterious effects of transposons, plants have acquired mechanisms to epigenetically silence them. Silenced Mu elements become heavily methylated, and their reactivation is very rare. To date, only UV-B radiation treatments have reactivated silenced Mu (Walbot 1999). We previously demonstrated that UV-B radiation modifies the chromatin at MuDR/Mu loci, triggering the expression of the transposase (Questa et al., 2010). MURA transposase interacts in vitro with a 32 bp domain, highly conserved in all mobile Mu TIRs (Benito and Walbot 1997). Furthermore, MURA can bind unmethylated, methylated and hemimethylated forms of its target sequence, therefore, the production of MURA is the rate-limiting step in reactivation of silent Mu elements. In the present work, we aim to elucidate the in vivo binding of MURA to its target sequence, and whether this interaction is affected by UV-B radiation.