Characterization of meiotic chromosome behavior in the autopolyploid Saccharum spontaneum reveals preferential chromosome pairing without distinct DNA sequence variation

Autopolyploidy and allopolyploidy may represent an evolutionary advantage and are more common in plants than assumed. However, less attention has been paid to autopolyploidy than to allopolyploidy, and its evolutionary consequences are largely unclear, especially for plants with high ploidy levels. In this study, we developed oligonucleotide (oligo)-based chromosome painting probes to identify individual chromosomes in S. spontaneum. Using fluorescence in situ hybridization (FISH), we investigated chromosome behavior during pachytene, metaphase, anaphase, and telophase of meiosis I (MI) in autotetraploid, autooctoploid, and autodecaploid S. spontaneum clones. All autopolyploid clones showed stable diploi-dized chromosome behavior; so that homologous chromosomes formed almost exclusively bivalents dur-ing MI. Two copies of homologous chromosome 8 with similar sizes in the autotetraploid clone showed preferential pairing with each other with respect to the other copies. However, sequence variation analysis showed no apparent differences among homologs of chromosome 8 and all other chromosomes. We suggest that either the stable diploidized pairing or the preferential pairing between homologous copies of chromosome 8 in the studied autopolyploid sugarcane are accounted for by unknown mechanisms other than DNA sequence similarity. Our results reveal evolutionary consequences of stable meiotic behavior in autopolyploid plants.(c) 2023 Crop Science Society of China and Institute of Crop Science, CAAS. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Autopolyploidy and allopolyploidy are common in plants, but autopolyploidy has received less attention and its evolutionary consequences are unclear. Using chromosome painting probes and fluorescence in situ hybridization, we studied chromosome behavior in autotetraploid, autooctoploid, and autodecaploid sugarcane clones. All autopolyploid clones exhibited stable diploidized chromosome behavior, with preferential pairing observed between homologous copies of chromosome 8. Sequence variation analysis showed no apparent differences among homologs of chromosome 8. Our results suggest that unknown mechanisms, other than DNA sequence similarity, contribute to stable meiotic behavior in these autopolyploid sugarcane plants.