In this ERC funded project we are focusing on developing breakthrough technologies to help maintain or improve the rate of genetic gain in crop varietal development.  Plant breeding is based on effectively shuffling genetic variation to generate new and improved combinations of alleles within and between chromosomes, and assembling them in a single superior genetic background.  However in the large genome Triticeae crop species wheat, barley and rye, our ability to shuffle alleles over large regions of the genome is compromised by a virtual absence of recombination (crossing over – CO).  This is particularly prominent in the peri-centromeric regions of each chromosome that may represent up to 70% of the physical length and contain up to 30% of the genes, and is mirrored in other large genome crops.

The ground-breaking challenge we are addressing in this project, is to release the genetic diversity present in the low recombining peri-centromeric regions of large cereal genomes.  Our strategy is to focus on understanding and exploiting the biological mechanisms that determine the frequency and distribution of meiotic crossing-over and the exchange of genetic material.

Figure 1. Schematic showing a. the barley genome b. location of genes on the genetic and d. physical maps with c. connecting lines. Gene density is shown on a heatmap scale: red- high, blue – low (Modified from IBSC 2012
Figure 1. Schematic showing a. the barley genome b. location of genes on the genetic and d. physical maps with c. connecting lines. Gene density is shown on a heatmap scale: red- high, blue – low (Modified from IBSC 2012

In sexually reproducing species, CO occurs during a special cell division called meiosis when the genetic content in the germ line is halved, with normal ploidy only restored upon fusion of male and female gametes.  This reduction in ploidy is achieved by two successive rounds of cell division relative to only one round of DNA replication.  At the first meiotic division, reciprocal exchange of genetic material by CO promotes correct segregation of homologous chromosomes by orienting them towards opposite poles.  Without COs, chromosomes segregate randomly during the first meiotic division, leading to aneuploidy (aberrant chromosome numbers) in the gametes and a subsequent decrease in fertility.  COs thus play an essential structural role during the sexual stage of the life cycle.  COs are also the main mechanism by which genetic diversity is shuffled – creating new genetic assortments of the organism’s parental DNA.  It is from these new assortments of alleles that locally adapted lineages emerge in response to environmental threat and improved plant varieties are selected during breeding.

Our research is focused on the model large-genome diploid inbreeding cereal crop plant barley.  Barley (2n=2x=14, genome size = 5.1Gbp) is an important crop plant grown widely throughout Europe and the rest of the world.  It underpins the brewing and distilling industries, is a key component of animal feed and remains subject of several intensive breeding efforts in the commercial sector.  The continuing elaboration of the barley genome has re-enforced understanding of the highly skewed distribution of CO towards the telomeric ends of barley chromosomes and the fact that up to a third of barley genes reside in peri-centromeric haplotype blocks that rarely, if ever, recombine (Figure 1).  Preliminary work has shown that investigating meiosis and CO in barley will reveal differences that are not observed in small genome models promoting a better understanding of the overall process.

Understanding meiosis in barley has the potential to deliver practical outcomes that will go well beyond the state of the art in breeding and genetics.  These will be immediately applicable in crop improvement without extensive, costly and uncertain translational efforts.  If successful they should transfer directly to related, but more difficult to study, cereal crops (e.g. hexaploid wheat).

This ERC project focuses on three critically important questions about CO in barley: 

Why is it restricted to the telomeric ends of chromosomes?

What proteins are the key players and what are their roles in controlling CO?

What strategies can be established to effectively increase or redistribute CO in CO-poor regions?

PrintFor further information on this project please contact Robbie Waugh (robbie.waugh@hutton.ac.uk) from the James Hutton Institute.