W521 Manipulating Crossover Frequency and Distribution in Barley

Date: Sunday, January 15, 2012
Time: 8:10 AM
Room: Pacific Salon 3
James Higgins , University of Birmingham, Birmingham, United Kingdom
Analysis in barley indicates that meiotic crossovers (COs) predominantly occur towards the ends of chromosomes thus disfavouring the generation of novel gene combinations and useful variation for breeding programs. We aim to elucidate these factors to manipulate CO frequency and distribution. In our initial analysis, antibodies raised against Arabidopsis meiotic proteins (including Asy1, ZYP1, RAD51, DMC1, MSH4 and MSH5) were used on barley, revealing an asymmetrical protein loading. Loading begins at the distal ends of the chromosomes and later in the interstitial and proximal regions. This suggests that COs are designated early in the distal regions such that interstitial sites are destined to be repaired via the non-CO pathway. An investigation into the asymmetrical loading revealed that euchromatin markers (H3K9me3, H3K27me3, H4K16ac) are highly enriched at the distal ends. Although the CO sites appear to correlate with these histone marks, this relationship is probably indirect. A bromo-deoxyuridine (BrdU) and ethynyl-deoxyuridine (EdU) time-course of pre-meiotic S-phase revealed that the euchromatic distal regions are replicated prior to the interstitial and proximal regions. It appears that the early replicating DNA in the distal regions enters meiosis first and sets up the protein loading asymmetry, which in turn sets up a CO bias in these regions. Also, during prophase I, the distal events coincide with phases of chromatin expansion whereas the interstitial and proximal sites occur during phases of contraction. Both genetically modified (GM) and non-GM approaches have been adopted to manipulate these processes, generating significantly more interstitial COs and occasionally proximal COs.