Repairing breaks in the plant genome: the importance of keeping it together

Contents   Summary 805 I. Introduction 806 II. Sources of DNA damage 806 III. The toxic effects of DSBs 806 IV. Detection of DSBs 806 V. Growth responses to genotoxic stress 809 VI. Chromatin structure and DSB repair 810 VII. Genome stability and environmental stress 811 VIII. Mechanisms of DSB repair 813 IX. Outlook 818   Acknowledgements 818   References 818 Summary DNA damage threatens the integrity of the genome and has potentially lethal consequences for the organism. Plant DNA is under continuous assault from endogenous and environmental factors and effective detection and repair of DNA damage are essential to ensure the stability of the genome. One of the most cytotoxic forms of DNA damage are DNA double-strand breaks (DSBs) which fragment chromosomes. Failure to repair DSBs results in loss of large amounts of genetic information which, following cell division, severely compromises daughter cells that receive fragmented chromosomes. This review will survey recent advances in our understanding of plant responses to chromosomal breaks, including the sources of DNA damage, the detection and signalling of DSBs, mechanisms of DSB repair, the role of chromatin structure in repair, DNA damage signalling and the link between plant recombination pathways and transgene integration. These mechanisms are of critical importance for maintenance of plant genome stability and integrity under stress conditions and provide potential targets for the improvement of crop plants both for stress resistance and for increased precision in the generation of genetically improved varieties.