Delineating the crossover control networks in plants

Abstract

Meiosis is a specialized type of cell division required for sexual reproduction. It ensures the reduction of the genome and the recombination of maternal and paternal chromosomal segments prior to the formation of generative cells. The process of meiotic recombination is initiated by programmed DNA double-strand breaks (DSBs), introduced by the conserved Spo11 protein. Ultimately, the positions of the DSBs define loci of mutual genetic exchange. However, in a single meiotic cell only a small sub-set of DSBs are destined to form genetic crossovers (COs), while the remainder are repaired via non-CO pathways. CO formation itself is subject to stringent control, which ensures that each homologue pair receives at least one obligate CO. A phenomenon known as CO interference then ensures that most (~85%) additional COs do not occur in an adjacent chromosomal region. As a result multiple COs are spaced well apart along the homologues. Understanding the factors that control DSB formation and processing to form COs is of fundamental scientific interest, moreover this knowledge will have important implications for manipulating meiotic recombination in crop plants.
In recent years meiosis research in plants has largely focussed on the identification of meiotic genes/proteins involved in recombination pathways or the organization of the chromosome axes and synaptonemal complex. Although these studies clearly demonstrate the importance of these proteins, it remained mostly enigmatic how their activities are coordinated to ensure the controlled formation of COs. Hence this collaborative project (DeCOP) seeks to shift emphasis to focus on how recombination, chromosome organisation and remodelling are orchestrated to control the frequency and distribution of COs. Specifically, we seek to identify the protein networks that determine the fate of individual DSBs and establish when CO interference is established. We propose to 1) perform an innovative screen to identify novel factors that modulate CO formation and interference, 2) investigate the role of chromosome axis-associated proteins in CO maturation and interference, 3) determine the role of (ATM/ATR mediated) phosphorylation in coordinating meiotic DNA repair and CO formation and 4) to identify proteins involved in the final step of CO formation.
The factors and processes studied in the DeCOP project will significantly enhance our understanding of the networks that govern crossover formation in plants. We therefore anticipate that our findings will strongly stimulate future crop breeding programmes.