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

Abstract

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.

Molecular domestication of transposable elements: From detrimental parasites to useful host genes

“…Evolutionary analysis of these genes has confirmed that the FHY3/FAR1 gene family has been co-opted from one or several related Mutator elements [41]. The maize Mutator transposase MURA is known to regulate the expression of both its own genes and occasionally adjacent genes [43][44][45]. Thus, it appears that FHY3 and FAR1 have retained the transcriptional activity of an ancestral Mutator transposase.…”

Changes to gene expression associated with hybrid speciation in plants: further insights from transcriptomic studies inSenecio

“…The widespread transposon activation proposed in McClintock's genome shock theory could also result in alterations to gene expression, either by knocking out gene activity or creating novel promoter function. Indeed, it has been shown that transposable elements can sometimes drive transcription if inserted upstream of a coding region (Barkan & Martiennssen 1991;Raizada et al 2001).…”

A maize MuDR transposon promoter shows limited autoregulation

“…The region at ±95 to ±124 (indicated in dark gray) has strong homology to histone hexamer and nonamer motifs as well as the B cyclin (MSA) enhancer. The region at position ±22 to ±76 (hatched box) shows high nucleotide sequence identity to the pollen enhancers of the tomato genes LAT59 and LAT52, and the maize gene ZM13 (M. Raizada et al 2001). B Plasmids used in this study.…”