Genetic variation is generated through homologous recombination during meiosis and underpins plant breeding efforts to deliver the rapid improvements in crops that will be required to ensure Food Security. HR is initiated by the formation of DNA double-strand breaks (DSBs) by the SPO11 complex. DSBs are processed by components of the HR pathway where they are repaired as crossovers (COs), which recombine the homologous parental chromosomes, or non-crossovers (NCOs), where only short stretches of DNA are exchanged. In plants most DSBs are repaired as NCOs. Moreover, the distribution of COs, notably in cereal crops, is localized to particular chromosomal regions. These limitations significantly lessen the genetic variation that can be generated in each meiotic division. Extensive studies by the MEIOREC investigators have led to significant progress in understanding the basis of these limitations and how they may be addressed. Nevertheless, a full understanding of the factors that control the transition of a DSB at a particular genomic locus to a CO and how this can be optimized has not yet been elucidated. We aim to decipher the molecular steps involved in the DSB to CO transition and evaluate strategies to manipulate CO formation using model species, thereby laying the foundation for subsequent translation of the most promising into crops. Our research will focus on three different stages in the control of CO formation in plants: (i) Factors controlling DSB formation: We will determine their minimum requirements. We will evaluate the potential of a MTOPVIB-CRISPR system as the basis for targeting DSBs complexes to recombination-cold regions. We will investigate the use of a suppression cassette (dCas9) and multiple short guide RNAs of the CO suppressor genes to enhance CO frequency. (ii) DSB processing, stable joint molecule formation and CO resolution: We will address how early steps in DSB processing and recombinase loading are linked and how this impacts on the CO/non-CO decision by analysing the role of the MRN complex and COM1 in the efficient removal of SPO11 from the DSB ends that is essential for loading of the DMC1 and RAD51 recombinases. We will also test the hypothesis that efficiency of CO formation in the recombination reaction can be influenced by Cas9-mediated targeting of the MUS81/GEN1 resolvases. (iii) Relationship of chromosome remodelling and CO formation: We will analyse the influence of posttranslational modifications of the chromosome axis in relation to CO formation and distribution. The inter-relationship between extensive remodelling of the chromosome axis and synaptonemal complex at the leptotene/zygotene transition and the maturation of CO designated recombination intermediates will be also analysed. The link between the programmed remodelling of the chromosome axis and CO distribution will be further investigated in barley and maize.