title: RAD51 loss of function abolishes gene targeting and de-represses illegitimate integration in the moss Physcomitrella patens.
abstract: Gene targeting (GT) is a major tool for basic and applied research during which the transforming DNA, which shares sequence homology with a chromosomal target, integrates at the corresponding locus by homologous recombination (HR). In eukaryotes, GT recruits enzymes from the HR-mediated double strand break repair pathway. Different mechanisms of HR have been described which depend on the Rad52 epistasis group of genes, but which specific mechanism is used by the cell for GT remains unclear. In Saccharomyces cerevisiae, the RAD52 protein is essential for GT, and the RAD51 protein plays a minor role. In filamentous fungi and animal cells, however, GT depends on RAD51 and is weakly affected by suppression of RAD52. Genetic evidence also indicates that the non-homologous end-joining pathway of DSB repair has a negative impact on GT efficiencies, but how the balance between these two pathways is controlled is poorly understood. Here, we have examined the role of RAD51 in the only plant that exhibits high GT frequencies, the model bryophyte Physcomitrella patens. Our results show that the two RAD51 proteins have partially redundant functions in the maintenance of genome integrity and resistance to ionizing radiation. Furthermore, we demonstrate that loss of function of the two RAD51 proteins completely abolishes GT and strongly increases illegitimate integration rates in this moss. These findings demonstrate for the first time in plant the critical role of RAD51 in controlling the balance between targeted and random integration events observed upon transgenesis, and confirm that P. patens is a particularly interesting tool for studying GT in higher eukaryotes.
authors.affiliation: Institut Jean-Pierre Bourgin, Station de Génétique et d'Amélioration des Plantes, UR254, INRA, Route de St Cyr, 78026 Versailles, France.
authors.forename: D G
authors.initials: DG
authors.lastname: Schaefer
authors.forename: F
authors.initials: F
authors.lastname: Delacote
authors.forename: F
authors.initials: F
authors.lastname: Charlot
authors.forename: N
authors.initials: N
authors.lastname: Vrielynck
authors.forename: A
authors.initials: A
authors.lastname: Guyon-Debast
authors.forename: S
authors.initials: S
authors.lastname: Le Guin
authors.forename: J M
authors.initials: JM
authors.lastname: Neuhaus
authors.forename: M P
authors.initials: MP
authors.lastname: Doutriaux
authors.forename: F
authors.initials: F
authors.lastname: Nogué
mesh_terms: D019068:Bryopsida / Q000235:genetics* / Q000378:metabolism* / Q000528:radiation effects; D004260:DNA Repair; D005720:Gamma Rays; D018390:Gene Targeting; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D051135:Rad51 Recombinase / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D014170:Transformation, Genetic
chemical_list: D010940:Plant Proteins; D051135:Rad51 Recombinase