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Polyploidy is a common feature in eukaryotes with one of paramount consequences leading to better environmental adaptation. Heterochromatin is often located at telomeres and centromeres and contains repetitive DNA sequences. Sainfoin (Onobrychis viciifolia) is an important perennial forage legume for sustainable agriculture. However, there are only a few studies on the sainfoin genome and chromosomes. In this study, novel tandem repetitive DNA sequences of the sainfoin genome (OnVi180, OnVi169, OnVi176 and OnVidimer) were characterized using bioinformatics, molecular and cytogenetic approaches. The OnVi180 and OnVi169 elements colocalized within functional centromeres. The OnVi176 and OnVidimer elements were localized in centromeric, subtelomeric and interstitial regions. We constructed a sainfoin karyotype that distinguishes the seven basic chromosome groups. Our study provides the first detailed description of heterochromatin and chromosome structure of sainfoin and proposes an origin of heterozygous ancestral genomes, possibly from the same ancestral diploid species, not necessarily from different species, or for chromosome rearrangements after polyploidy. Overall, we discuss our novel and complementary findings in a polyploid crop with unique and complex chromosomal features., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Bambara groundnut (Vigna subterranea L. Verdc.) is an un-derutilized minor legume crop with climate resilience and great potential use in world agriculture. This study aimed to cytogenetically characterize the genome and chromosome properties of Bambara groundnut. We cloned, sequenced, and mapped a 50-bp centromere-specific tandem repeat on all chromosomes. In addition, a 400-bp subtelomeric repeat was discovered and mapped on a single pair of chromosomes. A Bambara groundnut karyotype was constructed using these novel repeats along with ribosomal RNA genes (45S and 5S) and telomeric DNA sequences. This study provides the first analysis of the genome and chromosome properties of Bambara groundnut. We discuss our findings in relation to genetic improvement of Bambara groundnut and centromere evolution in legume species., (© 2022 S. Karger AG, Basel.)

The centromere is a structurally and functionally specialized region on each eukaryotic chromosome and is essential for accurate and complete segregation of chromosomes during cell division. Centromeric nucleosomes differ from canonical nucleosomes by replacement of the histone H3 with its centromere-specific variant CENH3. CENH3 is essential for active centromeres in most eukaryotes. Homologs of CENH3 are identified in many organisms. Sainfoin (Onobrychis viciifolia) is an agriculturally important perennial forage and is a legume of the Fabaceae family. There is very limited information on the structure of the sainfoin genome and no data are available on its centromere structure. Here, we aim to characterize the sainfoin CENH3 homolog (OvCENH3). Using a sequence homology-based strategy with gene-specific primers, we were able to clone transcripts from sainfoin total RNA. The amplified clones were sequenced and compared by bioinformatics tools. Four distinct alleles of OvCENH3 were detected. Our study provides the first structural features on sainfoin centromeres with a possible allotetraploid origin for sainfoin. We discuss and compare our findings with that for other important legume species.