The MuDR transposon terminal inverted repeat contains a complex plant promoter directing distinct somatic and germinal programs

Abstract

Summary The Mu transposons of maize are under stringent developmental control. Elements excise at high frequencies in terminally dividing somatic cells, but not in meristems. Mu elements in germinal cells amplify, without excision, and insert throughout the genome. All activities require MuDR, which encodes two genes, mudrA and mudrB, whose near‐identical promoters are located in the transposon terminal inverted repeats (TIR). We have fused the 216 bp TIR of the mudrB gene to GUS and luciferase reporters. We demonstrate that TIRB programs reporter expression in diverse, meristematic somatic cells, paradoxically in those cells in which Mu excisions are repressed. In germinal cells, immature tassel and mature pollen, reporter expression increases up to 20‐fold compared to leaf. By RNA blot hybridization, we demonstrate that endogenous mudrB and mudrA transcripts increase significantly in mature pollen; sequence comparisons demonstrate that the MuDR TIRs contain plant cell‐cycle enhancer motifs and functionally defined pollen enhancers. Therefore, the MuDR TIR promoters are developmentally regulated in both somatic and germinal tissues. Because database sequence analysis suggests that the MuDR TIR enhancers should be functional in both monocots and dicots, we suggest that the native MuDR promoter be used in attempts to transfer the unique behavior of Mu transposition to heterologous hosts.

Deletion Derivatives of the MuDR Regulatory Transposon of Maize Encode Antisense Transcripts but Are Not Dominant-Negative Regulators of Mutator Activities

“…Previous work established that a maize Ubi1 promoter is highly active in most maize tissues, including roots, developing anthers, and pollen (Raizada et al, 2001a). We confirmed that Ubi1 transcripts also are abundant in aleurone cells through 30 days after pollination ( Figure 5B), when mitotic proliferation has finished and when most Mu1 excisions have occurred (Levy and Walbot, 1990;Raizada and Walbot, 2000).…”

Mutator and MULE Transposons

“…Thus, it would appear that MURB is required for integration of Mutator elements, but not their excision. In situ analysis suggests that both mudrA and mudrB are expressed at highest levels in actively dividing cells and in pollen, consistent with the observation that the MuDR TIRs contain plant cell-cycle enhancer motifs and functionally defined pollen enhancers (16,22,23). Antibody analysis of MURB expression has shown that MURB protein is present at highest levels in actively dividing cells, particularly those in floral meristems, an observation that is consistent with in situ analysis of RNA expression (16,23).…”

The evolutionary fate of MULE-mediated duplications of host gene fragments in rice

“…Since the transcription start site for 153 of 235 transcripts that initiate within a MULE sequence is located <500 bp from the element terminus, the promoter is likely located within the TIR. In fact, the TIRs of the maize MuDR element harbor promoters for mudrA and mudrB (Raizada et al 2001), and while the TIR sequences of rice and maize MULEs are divergent, the majority of rice MULE TIRs contain putative TATA boxes and other promoter elements. In addition, transposition of MULEs with transduplicates may bring them into proximity to other cis-regulatory sequences.…”