Role of RAD51 in the repair of MuDR-induced double-strand breaks in maize (Zea mays L.)

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). Approximately 1% of the gametes from [RAD51.sup.+] plants that carry the MuDR-insertion allele al-m5216 include at least partial deletions of MuDR and the al gene. The structures of these deletions suggest they arise via the repair of MuDR-induced double-strand breaks via nonhomologous end joining. In RAD51 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 al-containing homolog. Together, these findings indicate that in [RAD51.sup.+] gel-minal cells MuDR-induced double-strand breaks (DSBs) are efficiently repaired via RAD51-directed homologous recombination with the sister chromatid. This suggests that [RAD51.sup.-] plants may offer an efficient means to generate deletion alleles for functional genomic studies. Additionally, the high proportion of Mu-active, [RAD51.sup.-] plants that exhibit severe developmental defects suggest that RAD51 plays a critical role in the repair of MuDR-induced DSBs early in vegetative development.