Originally published as Genetics Published Articles Ahead of Print on October 16, 2004.

Genetics, Vol. 169, 917-929, February 2005, Copyright © 2005
doi:10.1534/genetics.104.035089

MuDR Transposase Increases the Frequency of Meiotic Crossovers in the Vicinity of a Mu Insertion in the Maize a1 Gene

Marna D. Yandeau-Nelson^*, Qing Zhou^*,1, Hong Yao^*,2, Xiaojie Xu^,3, Basil J. Nikolau^*,, and Patrick S. Schnable^*,,,**,4

^* Interdepartmental Genetics Program, Cellular and Developmental Biology Program
Molecular, Cellular and Developmental Biology Program
Department of Biochemistry, Biophysics and Molecular Biology
Department of Agronomy, Iowa State University, Ames, Iowa 50011
^** Center for Plant Genomics, Iowa State University, Ames, Iowa 50011

⁴ Corresponding author: 2035B Roy J. Carver Co-Laboratory, Iowa State University, Ames, IA 50011.
E-mail: schnable{at}iastate.edu

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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