Identification of subtelomeric sequences with a possible role in chromosome recognition and pairing during meiosis in wheat

Abstract

The process of meiosis results in the formation of haploid daughter cells, each of which inherit a half of the diploid parental cells' genetic material. An appropriate homologue recognition is required to ensure ordered pairing and legitimate recombination during meiosis. In a polyploid such as bread wheat, (hexaploid, 2n=6x=42), which has three related genomes (A, B and D), the presence of homoeologous (related) chromosomes complicates the picture, since homologues also need to be distinguished from homoeologues (related) before the chromosomes can pair in an ordered way. The mechanism by which homologues identify one another is the most poorly understood aspect of meiosis. Recent observations have shown that the subtelomeric region plays a key role in the processes of homologue recognition and subsequent pairing during early meiosis in wheat, but the specific role of subtelomeres is still unclear. Unraveling the underlying molecular mechanisms involved will shed light to our understanding of how each chromosome associates with 'the right partner' during meiosis. The Wheat Genome Initiative has followed a flow cytometry strategy to separate 10 chromosomes one by one or in groups, the construction of a tiling BAC physical map, and subsequent sequencing of each chromosome using a BAC-by-BAC strategy. The limitations of a shotgun correct assembly and annotations of wheat genome hinder sequencing and assembly of large and repetitive genomes. Currently only a pseudochromosome for wheat chromosome 3B is available. Therefore, the Identification and molecular characterization of subtelomeric sequences in wheat chromosome arms is a challenge. The strategy we used consisted in consider a specific subtelomeric B-wheat probe contained in BAC clone 205008, which is located in the terminal bin 4BL-10 (0,95-1,0). In order to get a Chromosome 4BL contig including a subtelomeric region we used the application Blastn.sh in a MobaXterm Personal Edition v7.6 terminal screen connected to Picasso supercomputer (Genomics and Bioinformatics Platform of Andalusia, University of Málaga), which provides a basic set of Linux commands. A 5356 nt contig from chromosome 4BL was extracted from 4BL genomic chromosome arm using the BAC clone 205008 subtelomeric fragment. This strategy allowed us to isolate hypothetical subtelomeric contigs from the A, B and D wheat genomes. Currently we are validating by FISH the location of such subtelomeric probes in order to perform their molecular characterization.