A willow sex chromosome reveals convergent evolution of complex palindromic repeats
Carlson, Craig H
Jenkins, Jerry W
Tuskan, Gerald A
Smart, Lawrence B
DiFazio, Stephen P
AffiliationUniv Arizona, Sch Plant Sci, Arizona Genom Inst
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CitationZhou, R., Macaya-Sanz, D., Carlson, C.H. et al. A willow sex chromosome reveals convergent evolution of complex palindromic repeats. Genome Biol 21, 38 (2020). https://doi.org/10.1186/s13059-020-1952-4
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AbstractBackground Sex chromosomes have arisen independently in a wide variety of species, yet they share common characteristics, including the presence of suppressed recombination surrounding sex determination loci. Mammalian sex chromosomes contain multiple palindromic repeats across the non-recombining region that show sequence conservation through gene conversion and contain genes that are crucial for sexual reproduction. In plants, it is not clear if palindromic repeats play a role in maintaining sequence conservation in the absence of homologous recombination. Results Here we present the first evidence of large palindromic structures in a plant sex chromosome, based on a highly contiguous assembly of the W chromosome of the dioecious shrub Salix purpurea. The W chromosome has an expanded number of genes due to transpositions from autosomes. It also contains two consecutive palindromes that span a region of 200 kb, with conspicuous 20-kb stretches of highly conserved sequences among the four arms that show evidence of gene conversion. Four genes in the palindrome are homologous to genes in the sex determination regions of the closely related genus Populus, which is located on a different chromosome. These genes show distinct, floral-biased expression patterns compared to paralogous copies on autosomes. Conclusion The presence of palindromes in sex chromosomes of mammals and plants highlights the intrinsic importance of these features in adaptive evolution in the absence of recombination. Convergent evolution is driving both the independent establishment of sex chromosomes as well as their fine-scale sequence structure.
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Except where otherwise noted, this item's license is described as Copyright © The Author(s). 2020 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/). The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.