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Background  Mammalian BLM helicase is involved in DNA replication, DNA repair and homologous recombination (HR). These DNA transactions are associated tightly with cell division and are important for maintaining genome stability. However, unlike in mammals, cell division in higher plants is restricted mainly to the meristem, thus genome maintenance at the meristem is critical. The counterpart of  BLM  in  Arabidopsis  ( AtRecQ4A ) has been identified and its role in HR and in the response to DNA damage has been confirmed. However, the function of  AtRecQ4A  in the meristem during replication stress has not yet been well elucidated.    Results  We isolated the  BLM  counterpart gene  OsRecQl4  from rice and analyzed its function using a reverse genetics approach.  Osrecql4  mutant plants showed hypersensitivity to DNA damaging agents and enhanced frequency of HR compared to wild-type (WT) plants. We further analyzed the effect of aphidicolin—an inhibitor of S-phase progression via its inhibitory effect on DNA polymerases—on genome stability in the root meristem in  osrecql4  mutant plants and corresponding WT plants. The following effects were observed upon aphidicolin treatment: a) comet assay showed induction of DNA double-strand breaks (DSBs) in mutant plants, b) TUNEL assay showed enhanced DNA breaks at the root meristem in mutant plants, c) a recombination reporter showed enhanced HR frequency in mutant calli, d) propidium iodide (PI) staining of root tips revealed an increased incidence of cell death in the meristem of mutant plants.    Conclusions  These results demonstrate that the aphidicolin-sensitive phenotype of  osrecql4  mutants was in part due to induced DSBs and cell death, and that OsRecQl4 plays an important role as a caretaker, maintaining genome stability during DNA replication stress in the rice meristem.

DNA replication arrest leads to enhanced homologous recombination and cell death in meristems of rice OsRecQl4 mutants