13 ERA-CAPS. Delineating the crossover control networks in plants (DeCOP)

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 subset
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.

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 subset
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.

The significance and timeliness of the DeCOP programme stems from its potential to make a
significant contribution to global Food Security, which is one of the key challenges for the 21st
century. At present global population is predicted to increase by 2 billion to 9 billion by 2050. Based
on this it is anticipated that food production will need to increase by at least 50% to meet the demand
arising from this increase in population. This will require a concerted effort across a number of areas,
such as improved food distribution and storage facilities particularly in the developing world.
However, the delivery of a sustained improvement in crop yield will also be essential particularly as
crop yield will need to improved and safe-guarded against the impact of climate change. To deliver
improvement and sustainability in crop production it will be necessary to employ a range of
approaches. Although, GM may play an increasingly significant role, a major part in the delivery of
improved crop varieties will be based on classical breeding. This capitalizes on the natural genetic
variation that is generated by homologous recombination during meiosis. Meiotic recombination
creates new combinations of alleles that confer new phenotypes that can be tested for enhanced
performance. It is also essential in mapping genetic traits and in the introgression of new traits from
sources such as wild-crop varieties. It is increasingly apparent that our understanding of the factors
that control meiotic recombination in plants falls short of what is required if we are to overcome some
key problems. For example, it is not known why recombination in cereals and forage grasses is
skewed towards the ends of the chromosomes such that an estimated 30-50% of genes rarely, if ever,
recombine thereby limiting the genetic variation that is available to plant breeders. Understanding how
chromosome pairing and recombination are integrated is crucial particularly as many crop species are
polyploid which presents a further level of complexity. Existing links between the members of DeCOP
and plant breeding companies through current EU FP7 programmes, such as MeioSYS, RecBreed,
ensure that a route to achieving impact from the programme is established.