Meiosis in barley: manipulating crossover frequency and distribution

Lead Research Organisation: Aberystwyth University
Department Name: IBERS

Abstract

The future sustainability of UK agriculture will be dependent on the provision of new crop varieties that are able to meet future environmental and economic needs. The development of new crop varieties by plant breeding is based on harnessing the natural variation that is generated through the process of sexual reproduction and selective crossing to produce lines with novel combinations of desirable characteristics. During the formation of male and female gametes new combinations of the parental genes inherited by an individual are generated through the process of meiosis. In meiosis, homologous recombination ensures that chromosomes are accurately segregated such that each gamete gets a single complete set of chromosomes. To achieve this, transient physical links must be established between homologous pairs of parental chromosomes. This results in the reciprocal exchange of genetic information between each pair of homologous parental chromosomes, thereby generating a new combination of genes along each chromosome. Thus when male and female gametes fuse during sexual reproduction the progeny possess some characteristics of each parent and novel features that have arisen through the 'shuffling' of genes during meiotic recombination. Control of the patterns of recombination along chromosomes during meiosis in plants is therefore one of the major factors determining the outcome of plant breeding programmes. Unfortunately, it is clear that patterns of recombination can be highly skewed such that genes in some regions of the genome rarely undergo recombination. This is the case in some important grass species such as barley and wheat where it can have an adverse effect on potential breeding programmes Over the past decade studies in Arabidopsis, the model system for plant genetics, have resulted in considerable progress in our understanding of how meiosis and recombination in plants is controlled at the molecular level. Hence, this project seeks to transfer some of this knowledge to the crop plant barley and thus enable plant breeders to overcome one of the major challenges they face in the development of new varieties of this crop. This is feasible in the case of barley because we have a good understanding of barley genetics and genetic tools are in place for this crop to facilitate such a transfer. Our objectives will be to determine how meiotic recombination is controlled in barley and the basis for the skewed pattern of recombination. We will then explore strategies that could be used to manipulate the patterns of recombination that could be applied by plant breeders in their existing programmes without recourse to GM technology. If this is successful these approaches could then be applied to more complex grass crop species such as wheat and forage grasses (e.g. ryegrass) that show the same skewed distribution of recombination.

Technical Summary

Recent progress in understanding of the control of recombination in plants offers the prospect of the ability to manipulate this process to profoundly improve the speed and accuracy of plant breeding. This is particularly relevant for certain species in the grass subfamily Pooideae such as barley, wheat and ryegrass that show a highly skewed distribution of recombination relative to gene content. Currently the tools to manipulate this fundamental process in breeding programmes do not exist and the understanding of the control of recombination in grasses is fragmentary. Hence, this project seeks to take advantage of recent advances in meiosis research in Arabidopsis and apply this to barley as a representative cereal. This will allow the coupling of cytogenetic studies to the genetic and genomic resources available for this species and permit the use of forward and reverse genetic approaches to conduct functional analyses as has proved so fruitful in Arabidopsis. The project will involve initial work to transfer the molecular cytogenetic techniques and tools from Arabidopsis to barley which will enable a thorough molecular cytogenetic analysis of barley meiosis that will provide a benchmark against which to judge other aspects of the project. In parallel to the cytogenetic work barley homologues of known Arabidopsis meiotic genes need to be fully isolated and characterised through direct molecular analysis and bioinformatics work. These preparatory strands of work will then be utilised to determine and analyse factors affecting the frequency and distribution of meiotic crossovers in barley lines using both existing and de novo mutants in both forward and reverse genetic approaches. The results from this work will inform the strategies used in the final suite of work aimed at the manipulation of recombination these will include the use of TILLING as well as transformation approaches to provide the possibility of future non-GM exploitation routes.

Publications

10 25 50
 
Description A sizeable proportion of the genes of many agronomically important cereal and grass species, such as wheat, rye barley and ryegrass, is locked into regions of the genome which rarely, if ever, recombine during meiosis. This pattern of recombination caps genetic variation, reinforces linkage drag in introgression programmes, and reduces the effectiveness of map-based cloning approaches. Potentially, much is to be gained by shifting sites of crossing over to release novel genetic variation from which new phenotypes may be selected in advanced breeding programmes. This project is part of a collaborative LoLa programme with three other institutions to understand and exploit the factors which govern the patterns of recombination in barley. The main findings of this study are:

1. Non-homologous centromeres are coupled prior to synapsis of chromosomes during meiosis.

2. Key structural proteins of meiosis are expressed and loaded preferentially at the ends of chromosomes, and may predispose these regions to recombination.

3. Synaptic initiation sites are added as meiosis proceeds.

4. Structured illumination microscopy reveals for the first time two different configurations of the synaptonemal complex (the protein structure which holds homologous chromosomes together during meiosis).

5. Barley has at least two different crossover pathways, as in the model plant Arabidopsis.

6. There are significant differences in crossover frequencies between barley cultivars.

7. Interference in barley is relatively weak compared to other plant species.

8. Elevation of growth temperature during meiosis has a significant effect upon the distribution of crossovers.
Exploitation Route Recruitment of genes not normally involved in recombination could provide a new means of generating genetic variation for use in pre-breeding programmes. 1. The differences in recombination between cultivars could be exploited in genetic mapping studies to isolate new genes controlling the frequency and distribution of crossovers.

2. The relatively facile manipulation of recombination in barley by raising the growth temperature has potential in pre-breeding programmes to generate novel genotypes.
Sectors Agriculture, Food and Drink

 
Description They have been used in the design of a work package of an ISPG
First Year Of Impact 2013
Sector Agriculture, Food and Drink
 
Description Eucarpia Festulolium group 
Organisation DLF Trifolium
Country Czech Republic 
Sector Private 
PI Contribution Trialing sites and Festulolium cultivars from the UK
Collaborator Contribution Trialing sites and Festulolium cultivars from across Europe
Impact Paper in preparation. Associated with reports and workshops and successive Eucarpia meetings
Start Year 2012
 
Description Eucarpia Festulolium group 
Organisation French National Institute of Agricultural Research
Country France 
Sector Public 
PI Contribution Trialing sites and Festulolium cultivars from the UK
Collaborator Contribution Trialing sites and Festulolium cultivars from across Europe
Impact Paper in preparation. Associated with reports and workshops and successive Eucarpia meetings
Start Year 2012
 
Description Eucarpia Festulolium group 
Organisation Institute for Agricultural and Fisheries Research
Country Netherlands 
Sector Academic/University 
PI Contribution Trialing sites and Festulolium cultivars from the UK
Collaborator Contribution Trialing sites and Festulolium cultivars from across Europe
Impact Paper in preparation. Associated with reports and workshops and successive Eucarpia meetings
Start Year 2012
 
Description Eucarpia Festulolium group 
Organisation Institute for Medicinal Plant Research Kruševac (IKBKS)
Country Serbia 
Sector Charity/Non Profit 
PI Contribution Trialing sites and Festulolium cultivars from the UK
Collaborator Contribution Trialing sites and Festulolium cultivars from across Europe
Impact Paper in preparation. Associated with reports and workshops and successive Eucarpia meetings
Start Year 2012
 
Description Eucarpia Festulolium group 
Organisation Norwegian Institute for Agricultural and Environmental Research
Country Norway 
Sector Public 
PI Contribution Trialing sites and Festulolium cultivars from the UK
Collaborator Contribution Trialing sites and Festulolium cultivars from across Europe
Impact Paper in preparation. Associated with reports and workshops and successive Eucarpia meetings
Start Year 2012
 
Description Eucarpia Festulolium group 
Organisation Polish Academy of Sciences
Department Institute of Plant Genetics
Country Poland 
Sector Academic/University 
PI Contribution Trialing sites and Festulolium cultivars from the UK
Collaborator Contribution Trialing sites and Festulolium cultivars from across Europe
Impact Paper in preparation. Associated with reports and workshops and successive Eucarpia meetings
Start Year 2012
 
Description Eucarpia Festulolium group 
Organisation Rothamsted Research
Country United Kingdom 
Sector Academic/University 
PI Contribution Trialing sites and Festulolium cultivars from the UK
Collaborator Contribution Trialing sites and Festulolium cultivars from across Europe
Impact Paper in preparation. Associated with reports and workshops and successive Eucarpia meetings
Start Year 2012
 
Description Eucarpia Festulolium group 
Organisation Teagasc
Department Teagasc Food Research Centre
Country Ireland 
Sector Academic/University 
PI Contribution Trialing sites and Festulolium cultivars from the UK
Collaborator Contribution Trialing sites and Festulolium cultivars from across Europe
Impact Paper in preparation. Associated with reports and workshops and successive Eucarpia meetings
Start Year 2012
 
Description UCAS visit days and Open Days 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Informal talk to prospective students and their parents, using my own research as an example of the linkage between my research and teaching.
Year(s) Of Engagement Activity 2012,2013,2014,2015,2016
 
Description lecture (Aberystwyth) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Undergraduate students
Results and Impact Formal lecture in my level 2 module Chromosome Dynamics to illustrate the application of genetics to improve crops. The lecture stimulated interest in my projects at level 3, and has resulted in an application for a Genes and Development Summer Studentship.
Year(s) Of Engagement Activity 2014,2015,2016