Role of RAD51 in the Repair of MuDR-Induced Double-Strand Breaks in Maize (Zea mays L.)

Jin Li^*^,^,1, Tsui-Jung Wen^,2 and Patrick S. Schnable^*^,^,^,^,3

^* Department of Genetics, Development, and Cell Biology, Interdepartmental Genetics Graduate Program, Department of Agronomy and Center for Plant Genomics, Iowa State University, Ames, Iowa 50011

^³ Corresponding author: 2035B Roy J. Carver Co-Lab, Iowa State University, Ames, IA 50011.
E-mail: schnable{at}iastate.edu

Rates of Mu transposon insertions and excisions are both highin late somatic cells of maize. In contrast, although high ratesof insertions are observed in germinal cells, germinal excisionsare recovered only rarely. Plants doubly homozygous for deletionalleles of rad51A1 and rad51A2 do not encode functional RAD51protein (RAD51^–). Approximately 1% of the gametes fromRAD51⁺ plants that carry the MuDR-insertion allele a1-m5216include at least partial deletions of MuDR and the a1 gene.The structures of these deletions suggest they arise via therepair of MuDR-induced double-strand breaks via nonhomologousend joining. In RAD51^– plants these germinal deletionsare recovered at rates that are at least 40-fold higher. Theserates are not substantially affected by the presence or absenceof an a1-containing homolog. Together, these findings indicatethat in RAD51⁺ germinal cells MuDR-induced double-strand breaks(DSBs) are efficiently repaired via RAD51-directed homologousrecombination with the sister chromatid. This suggests thatRAD51^– plants may offer an efficient means to generatedeletion alleles for functional genomic studies. Additionally,the high proportion of Mu-active, RAD51^– plants that exhibitsevere developmental defects suggest that RAD51 plays a criticalrole in the repair of MuDR-induced DSBs early in vegetativedevelopment.