Most cited article - PubMed ID 25349265
Extensive pericentric rearrangements in the bread wheat (Triticum aestivum L.) genotype "Chinese Spring" revealed from chromosome shotgun sequence data
The hexaploid wheat genotype Chinese Spring (CS) has been used worldwide as the reference base for wheat genetics and genomics, and significant resources have been used by the international community to generate a reference wheat genome based on this genotype. By sequencing flow-sorted 3B chromosome from a hexaploid wheat genotype CRNIL1A and comparing the obtained sequences with those available for CS, we detected that a large number of sequences in the former were missing in the latter. If the distribution of such sequences in the hexaploid wheat genome is random, CRNILA sequences missing in CS could be as much as 159.3 Mb even if only fragments of 50 bp or longer were considered. Analysing RNA sequences available in the public domains also revealed that dispensable genes are common in hexaploid wheat. Together with those extensive intra- and interchromosomal rearrangements in CS, the existence of such dispensable genes is another factor highlighting potential issues with the use of reference genomes in various studies. Strong deviation in distributions of these dispensable sequences among genotypes with different geographical origins provided the first evidence indicating that they could be associated with adaptation in wheat.
BACKGROUND: Chromosomal rearrangements are a major driving force in shaping genome during evolution. Previous studies show that translocated genes could undergo elevated rates of evolution and recombination frequencies around these genes can be altered. Based on the recently released genome sequences of Triticum urartu, Aegilops tauschii, Brachypodium distachyon and bread wheat, an analysis of interchromosomal translocations in the hexaploid wheat genotype 'Chinese Spring' ('CS') was conducted based on chromosome shotgun sequences from individual chromosome arms of this genotype. RESULTS: A total of 720 genes representing putative interchromosomal rearrangements was identified. They were distributed across the 42 chromosome arms. About 59% of these translocated genes were those involved in the well-characterized translocations involving chromosomes 4A, 5A and 7B. The other 41% of the genes represent a large numbers of putative interchromosomal rearrangements which have not yet been described. The number of the putative translocation events in the D subgenome was about half of those presented in either the A or B subgenomes, which agreed well with that the times of interaction between the A and B subgenomes almost doubled that between either of them and the D subgenome. CONCLUSIONS: The possible existence of a large number of interchromosomal rearrangements detected in this study provide further evidence that caution should be taken when using synteny in ordering sequence contigs or in cloning genes in hexaploid wheat. The identification of these putative translocations in 'CS' also provide a base for a systematic evaluation of their presence or absence in the full spectrum of bread wheat and its close relatives, which could have significant implications in a wide array of fields ranging from studies of systematics and evolution to practical breeding.
