MuDR transposase increases the frequency of meiotic crossovers in the vicinity of a Mu insertion in the maize a1 gene - PubMed (original) (raw)

MuDR transposase increases the frequency of meiotic crossovers in the vicinity of a Mu insertion in the maize a1 gene

Marna D Yandeau-Nelson et al. Genetics. 2005 Feb.

Erratum in

Abstract

Although DNA breaks stimulate mitotic recombination in plants, their effects on meiotic recombination are not known. Recombination across a maize a1 allele containing a nonautonomous Mu transposon was studied in the presence and absence of the MuDR-encoded transposase. Recombinant A1' alleles isolated from a1-mum2/a1::rdt heterozygotes arose via either crossovers (32 CO events) or noncrossovers (8 NCO events). In the presence of MuDR, the rate of COs increased fourfold. This increase is most likely a consequence of the repair of MuDR-induced DNA breaks at the Mu1 insertion in a1-mum2. Hence, this study provides the first in vivo evidence that DNA breaks stimulate meiotic crossovers in plants. The distribution of recombination breakpoints is not affected by the presence of MuDR in that 19 of 24 breakpoints isolated from plants that carried MuDR mapped to a previously defined 377-bp recombination hotspot. This result is consistent with the hypothesis that the DNA breaks that initiate recombination at a1 cluster at its 5' end. Conversion tracts associated with eight NCO events ranged in size from <700 bp to >1600 bp. This study also establishes that MuDR functions during meiosis and that ratios of CO/NCO vary among genes and can be influenced by genetic background.

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Figures

F<sc>igure</sc> 1.—

Figure 1.—

Isolation of intragenic recombinant _A1_′ alleles. The parents of and the progeny resulting from crosses 1–2 are illustrated. Chromosomes from the a1-mum2 and a1::rdt sh2 stocks are illustrated in black and gray, respectively. The RFLP marker php10080 and the a1 and sh2 genes are represented by black (if derived from a1-mum2 chromosome) or gray (if derived from a1::rdt chromosome) boxes. Triangles indicate the positions of Mu1 and rdt transposon insertions in the a1 gene. Class III and IV COs arise following DNA breaks on either chromosome. Class V and VI NCOs arise following breaks on the _a1::rdt_- and _a1-mum2_-containing chromosomes, respectively. Only the colored shrunken recombinants (classes III and V) were characterized in this study. Class I progeny will be spotted if they carry MuDR.

F<sc>igure</sc> 2.—

Figure 2.—

Physical mapping of CO breakpoints and NCO conversion tracts. (A) Schematic of the a1-mum2 and a1::rdt alleles in which boxes and triangles represent exons and transposon insertions, respectively. The RFLP marker php10080 and the sh2 locus are proximal and distal to the a1 locus, respectively. The positions of primers used for PCR amplification and sequencing and the diagnostic _Pst_I site are indicated. The a1 gene is separated into 23 intervals defined by the 24 polymorphisms (vertical lines) between the a1::rdt and a1-mum2 alleles. The width of a given vertical bar is proportional to the number of base pairs involved in the polymorphism. The 3′-most polymorphic site (a 32-bp insertion/deletion) is indicated by an asterisk. Sequences 1059 bp 3′ of this site are identical between the a1::rdt and a1-mum2 alleles. (B) Locations of CO recombination breakpoints associated with _A1_′ alleles. Intervals are defined by the polymorphic sites shown in A. The numbers of recombination breakpoints that resolved in each interval are indicated. The 377-bp recombination hotspot identified previously (X

u

et al. 1995) is indicated. Data from X

u

et al. (1995) are provided for reference. (C) Locations of NCO conversion endpoints and sizes of conversion tracts associated with eight _A1_′ alleles isolated from crosses 1 and 2. When possible, conversion tract endpoints were mapped relative to pairs of DNA sequence polymorphisms. Sequences confirmed to be included in the conversion tract are measured in base pairs above the bold lines. Conversion tract endpoints can be positioned relative to the nearest polymorphism and the size of the tract is equal to or less than the length of the thin line. The proximal ends of four conversion tracts (arrows on left side of bold lines) lie to the proximal side of the polymorphic site indicated by an asterisk in A. The numbers of _A1_′ alleles with the indicated type of conversion tract are indicated on the right.

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References

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