Successful and efficient plant breeding depends on rapid recombination of advantageous traits to form new crop varieties. In recent years new breeding techniques have been introduced which rely on transgenic alteration of somatic cells and regeneration into plants with novel properties. The precision and effectiveness of both strategies rely upon homologous recombination (HR). The objective of this proposal is to provide plant breeders with new tools allowing better control over HR in both somatic and meiotic cells. The expected outcomes of the proposed research are efficient gene targeting (GT) technologies for precise engineering of plant genomes and control of rates of meiotic recombination between homologous or homeologous chromosomes in classical breeding. The major components of the HR machinery are common to somatic and meiotic cells, enabling us to address both processes in a synergistic way. HR can be divided into different steps: initiation by formation of a DNA double-strand break (DSB); recognition and invasion of an homologous DNA sequence; resolution of recombination structures. Each stage contains a bottleneck for both GT and meiotic HR that we will address. Work package 1 (WP1) aims at enhancing HR through targeted DSB induction. DSBs will be induced by Zinc-finger nucleases that can be custom-designed for target sequences anywhere in the genome. In WP2, we will test the influence of HR factors affecting homologue invasion and heteroduplex formation, such as RAD51 and its paralogues, the RAD52 homologue, genes that affect cytosine methylation in DNA, and mismatch repair. In WP3 we will concentrate on proteins involved in resolution and crossing-over. WP4 will test combinations of those approaches found in the first three WPs to build optimal strategies for application. Most experiments will be performed in the model plant Arabidopsis and implemented into crops such as tomato and maize to guarantee quick applicability for breeding.