title: Recurrent sequence exchange between homeologous grass chromosomes.
abstract: All grass species evolved from an ancestor that underwent a whole-genome duplication (WGD) approximately 70 million years ago. Interestingly, the short arms of rice chromosomes 11 and 12 (and independently their homologs in sorghum) were found to be much more similar to each other than other homeologous regions within the duplicated genome. Based on detailed analysis of rice chromosomes 11 and 12 and their homologs in seven grass species, we propose a mechanism that explains the apparently 'younger' age of the duplication in this region of the genome, assuming a small number of reciprocal translocations at the chromosome termini. In each case the translocations were followed by unbalanced transmission and subsequent lineage sorting of the involved chromosomes to offspring. Molecular dating of these translocation events also allowed us to date major chromosome 'fusions' in the evolutionary lineages that led to Brachypodium and Triticeae. Furthermore, we provide evidence that rice is exceptional regarding the evolution of chromosomes 11 and 12, inasmuch as in other species the process of sequence exchange between homeologous chromosomes ceased much earlier than in rice. We presume that random events rather than selective forces are responsible for the observed high similarity between the short arm ends of rice chromosomes 11 and 12.
authors.affiliation: Institute of Plant Biology, University of Zurich, Zollikerstrasse 107, Zurich, CH-8008, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wicker
authors.affiliation: Arizona Genomics Institute, School of Plant Sciences, University of Arizona, Tucson, AZ, USA.
authors.forename: Rod A
authors.initials: RA
authors.lastname: Wing
authors.affiliation: Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Gatersleben, Stadt Seeland, D-06466, Germany.|Central European Institute of Technology (CEITEC) and Faculty of Science, Masaryk University, Brno, 62500, Czech Republic.
authors.forename: Ingo
authors.initials: I
authors.lastname: Schubert
mesh_terms: D001483:Base Sequence; D032461:Chromosomes, Plant / Q000235:genetics*; D019143:Evolution, Molecular; D020440:Gene Duplication; D014644:Genetic Variation; D018745:Genome, Plant / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D006109:Poaceae / Q000145:classification / Q000235:genetics*; D011995:Recombination, Genetic; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D026801:Synteny; D013997:Time Factors; D014178:Translocation, Genetic
keywords: genome evolution; grass ancestor; inter-homeolog recombination; reciprocal translocation; whole-genome duplication