Quantitative high resolution mapping of HvMLH3 foci in barley pachytene nuclei reveals a strong distal bias and weak interference

• Published in: Journal of experimental botany Vol. 64; no. 8; pp. 2139 - 2154
• Main Authors: Phillips, Dylan, Wnetrzak, Joanna, Nibau, Candida, Barakate, Abdellah, Ramsay, Luke, Wright, Frank, Higgins, James D, Perry, Ruth M, Jenkins, Glyn
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press [etc.] 01.05.2013; Oxford University Press
• Subjects: Arabidopsis - genetics; Barley; Base Sequence; Biological and medical sciences; breeding; Centromeres; chiasmata; Chromosome Mapping; Chromosomes; Chromosomes, Plant - genetics; Chromosomes, Plant - physiology; Crossing Over, Genetic - genetics; Crossing Over, Genetic - physiology; Crossover interference; Crossovers; cultivars; fluorescence in situ hybridization; Fundamental and applied biological sciences. Psychology; genes; Genetic Linkage - genetics; Genetic Linkage - physiology; Genetic Loci - genetics; Genetic Loci - physiology; Genetic mapping; genetic variation; Genetics; Genome, Plant - genetics; Genome, Plant - physiology; Genomes; Hordeum - genetics; Hordeum - physiology; Hordeum vulgare; In Situ Hybridization, Fluorescence; landscapes; molecular cloning; Molecular Sequence Data; Pachytene stage; Pachytene Stage - genetics; Pachytene Stage - physiology; Phylogeny; Plant physiology and development; RESEARCH PAPER; Ribosomal DNA; Sequence Alignment; synaptonemal complex; Synaptonemal Complex - genetics; Synaptonemal Complex - physiology; Cartography; Barley; Monocotyledones; High resolution; crossover; Hordeum vulgare; Bias; Cereal crop; MLH3; Gramineae; Angiospermae; Botany; Spermatophyta; interference; chiasma
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/ert079

In barley (Hordeum vulgare L.), chiasmata (the physical sites of genetic crossovers) are skewed towards the distal ends of chromosomes, effectively consigning a large proportion of genes to recombination coldspots. This has the effect of limiting potential genetic variability, and of reducing the efficiency of map-based cloning and breeding approaches for this crop. Shifting the sites of recombination to more proximal chromosome regions by forward and reverse genetic means may be profitable in terms of realizing the genetic potential of the species, but is predicated upon a better understanding of the mechanisms governing the sites of these events, and upon the ability to recognize real changes in recombination patterns. The barley MutL Homologue (HvMLH3), a marker for class I interfering crossovers, has been isolated and a specific antibody has been raised. Immunolocalization of HvMLH3 along with the synaptonemal complex transverse filament protein ZYP1, used in conjunction with fluorescence in situ hybridization (FISH) tagging of specific barley chromosomes, has enabled access to the physical recombination landscape of the barley cultivars Morex and Bowman. Consistent distal localization of HvMLH3 foci throughout the genome, and similar patterns of HvMLH3 foci within bivalents 2H and 3H have been observed. A difference in total numbers of HvMLH3 foci between these two cultivars has been quantified, which is interpreted as representing genotypic variation in class I crossover frequency. Discrepancies between the frequencies of HvMLH3 foci and crossover frequencies derived from linkage analysis point to the existence of at least two crossover pathways in barley. It is also shown that interference of HvMLH3 foci is relatively weak compared with other plant species.