The Mutator Transposable Element System of Maize

Bennetzen, Jeffrey L.

doi:10.1007/978-3-642-79795-8_9

Cited by 94 publications

(87 citation statements)

References 120 publications

(152 reference statements)

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“…As shown in Figure 6B, hMuDR FspI sequences were heavily methylated in non-Mutator lines. Consistent with expectations from previous DNA methylation studies at the TIRs of Mu1 and MuDR elements (Bennetzen, 1996), partial demethylation of one or both FspI sites in some homologs was observed in active Mutator stocks. Therefore, a subset of hMuDR elements appears to be transcriptionally active despite epigenetic modification.…”

Section: Transcription Properties Of Hmudr and Mudr Elementssupporting

confidence: 91%

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Expression and Post-Transcriptional Regulation of Maize Transposable Element MuDR and Its Derivatives

Rudenko¹,

Walbot²

2001

The Plant Cell

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The transposition of Mu elements underlying Mutator activity in maize requires a transcriptionally active MuDR element. Despite variation in MuDR copy number and RNA levels in Mutator lines, transposition events are consistently late in plant development, and Mu excision frequencies are similar. Here, we report previously unsuspected and ubiquitous MuDR homologs that produce both RNA and protein. MuDR transcript levels are proportional to MuDR copy number, and homolog transcript levels increase in active Mutator lines. A subset of homologs exhibits constitutive transcription in MuDR Ϫ and epigenetically silenced MuDR lines, suggesting independent transcriptional regulation. Surprisingly, immunodetection demonstrated nearly invariant levels of MuDR and homolog protein products in all tested Mutator and non-Mutator stocks. These results suggest a strict control over protein production, which might explain the uniform excision frequency of Mu elements. Moreover, the nonfunctional proteins encoded by homologs may negatively regulate Mutator activity and represent part of the host defense against this transposon family. INTRODUCTIONOptimized transmission and restricted transposition activity are characteristics of many transposable elements. These features combine to allow efficient transposon proliferation with a minimal cost to the host genome. A variety of regulatory mechanisms operating at both the transcriptional and post-transcriptional levels can result in specific temporal and spatial patterns of transposon activity. Some mechanisms are epigenetic and act through several generations. In plants, increased DNA methylation of promoter regions of autonomous elements such as Ac , En / Spm , and MuDR correlates with decreased production of transposase transcripts and loss of transposition reactions (Fedoroff and Chandler, 1994; Martienssen and Baron, 1994). In some cases, host methylation acts in concert with transposon autoregulation. For example, the TnpA transposase protein encoded by Spm binds to its own unmethylated promoter, an interaction that decreases transcription; in the absence of Spm -encoded products, the promoter becomes methylated, and both transcription and transposition cease (Schläppi et al., 1994). Introduction of a functional Spm element results in activation of the silenced promoter and resumption of transposon activity.More dynamic regulation occurs during a single life cycle to limit the production or function of active transposase proteins.For example, tissue-specific RNA splicing restricts expression of the functional transposase of the Drosophila melanogaster P element to the germ line (Laski et al., 1986;Siebel et al., 1992). In bacteria, the inhibition of bacterial Tn10 transposition occurs through production of element-encoded antisense RNA (Simons and Kleckner, 1988). The maize transposable element Ac exhibits a negative dosage phenomenon: with increasing copy number and RNA levels, there is a lower excision frequency, and transposition events occur later in development (McClintock, 1...

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Section: Transcription Properties Of Hmudr and Mudr Elementssupporting

confidence: 91%

“…As shown in Figure 3A, all mudrA and the mudrB homologs except hmudrA8 and hmudrA9, the Mu5-like elements, cluster with MuDR and are distinct from other known Mu subfamilies (Bennetzen, 1996).…”

Section: Organization Of Mudrb and Mudra Homologous Genesmentioning

confidence: 95%

Expression and Post-Transcriptional Regulation of Maize Transposable Element MuDR and Its Derivatives

Rudenko¹,

Walbot²

2001

The Plant Cell

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“…In contrast to the low rate of germinal reversions, germinal insertions of Mu transposons occur frequently (Chandler and Hardeman 1992;Bennetzen 1996;Lisch 2002;Walbot and Rudenko 2002). Model A explains this apparent discrepancy in germinal excision and insertion rates by invoking highly efficient HR-mediated repair of the MuDR-induced DSBs associated with the excision of Mu transposons (Figure 1).…”

Section: Resultsmentioning

confidence: 99%

“…The MuDR element carries the mudrA, which is required for transacting transposase activity (reviewed by Chandler and Hardeman 1992;Bennetzen 1996;Lisch 2002;Walbot and Rudenko 2002). In germinal cells, Mu transposition frequencies can be as high as more than once per element per plant generation (Alleman and Freeling 1986;Walbot and Warren 1988).…”

mentioning

confidence: 99%

Role of RAD51 in the Repair ofMuDR-Induced Double-Strand Breaks in Maize (Zea maysL.)

Jin

Wen²,

Schnable

2008

Genetics

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Rates of Mu transposon insertions and excisions are both high in late somatic cells of maize. In contrast, although high rates of insertions are observed in germinal cells, germinal excisions are recovered only rarely. Plants doubly homozygous for deletion alleles of rad51A1 and rad51A2 do not encode functional RAD51 protein (RAD51 À ). Approximately 1% of the gametes from RAD51 1 plants that carry the MuDRinsertion allele a1-m5216 include at least partial deletions of MuDR and the a1 gene. The structures of these deletions suggest they arise via the repair of MuDR-induced double-strand breaks via nonhomologous end joining. In RAD51À plants these germinal deletions are recovered at rates that are at least 40-fold higher. These rates are not substantially affected by the presence or absence of an a1-containing homolog. Together, these findings indicate that in RAD511 germinal cells MuDR-induced double-strand breaks (DSBs) are efficiently repaired via RAD51-directed homologous recombination with the sister chromatid. This suggests that RAD51À plants may offer an efficient means to generate deletion alleles for functional genomic studies. Additionally, the high proportion of Mu-active, RAD51À plants that exhibit severe developmental defects suggest that RAD51 plays a critical role in the repair of MuDR-induced DSBs early in vegetative development.

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“…Like the Ac/Ds and Spm/dSpm systems, Mutator activity is regulated by the two-component system composed of two DNA-type transposable elements, MuDR and Mu (Bennetzen 1996). MuDR is an autonomous element, while Mu is a non-autonomous deletion derivative of MuDR.…”

Section: Introductionmentioning

confidence: 99%

Sequence diversity and copy number variation of Mutator-like transposases in wheat

et al. 2008

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Partial transposase-coding sequences of Mutator-like elements (MULEs) were isolated from a wild einkorn wheat, Triticum urartu, by degenerate PCR. The isolated sequences were classified into a MuDR or Class I clade and divided into two distinct subclasses (subclass I and subclass II). The average pair-wise identity between members of both subclasses was 58.8% at the nucleotide sequence level. Sequence diversity of subclass I was larger than that of subclass II. DNA gel blot analysis showed that subclass I was present as low copy number elements in the genomes of all Triticum and Aegilops accessions surveyed, while subclass II was present as high copy number elements. These two subclasses seemed uncapable of recognizing each other for transposition. The number of copies of subclass II elements was much higher in Aegilops with the S, S l and D genomes and polyploid Triticum species than in diploid Triticum with the A genome, indicating that active transposition occurred in S, S l and D genomes before polyploidization. DNA gel blot analysis of six species selected from three subfamilies of Poaceae demonstrated that only the tribe Triticeae possessed both subclasses. These results suggest that the differentiation of these two subclasses occurred before or immediately after the establishment of the tribe Triticeae.

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The Mutator Transposable Element System of Maize

Cited by 94 publications

References 120 publications

Expression and Post-Transcriptional Regulation of Maize Transposable Element MuDR and Its Derivatives

Expression and Post-Transcriptional Regulation of Maize Transposable Element MuDR and Its Derivatives

Role of RAD51 in the Repair ofMuDR-Induced Double-Strand Breaks in Maize (Zea maysL.)

Sequence diversity and copy number variation of Mutator-like transposases in wheat

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