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Genetic research

Breakthrough in Legume Genomics: Complete and Accurate Genome Assemblies for Medicago

Strategic Insights

— 2 min read

Researchers at the Chinese Academy of Sciences' Institute of Genetics and Developmental Biology have made a groundbreaking discovery in legume genomics by producing the first gap-free, telomere-to-telomere (T2T) genome assemblies for two model Medicago species, Medicago truncatula Jemalong A17 and Medicago littoralis R108. These assemblies span 494.47 Mb and 415.27 Mb, respectively, with 99% completeness based on BUSCO assessment, representing the most complete genomes available for the Medicago genus to date. The study provides an unprecedented view into the structure and evolution of plant centromeres, offering a valuable reference for legume functional genomics and precision breeding.

Key Takeaways:

  • The researchers successfully constructed T2T genome assemblies for Medicago truncatula Jemalong A17 (A17 v6.0) and Medicago littoralis R108 (R108 v3.0) using a combination of PacBio HiFi sequencing, ultra-long Oxford Nanopore reads, and Hi-C chromatin conformation capture.
  • The assemblies span 494.47 Mb and 415.27 Mb, respectively, with 99% completeness based on BUSCO assessment, representing the most complete genomes available for the Medicago genus to date.
  • The study decodes the centromere, a central region of eukaryotic genomes, which plays a key role in chromosome segregation, and reveals striking differences between the centromeres of A17 and R108.
  • The researchers identified several highly chromosome-specific satellite repeats (e.g., CentM51, CentM515, CentM287) and propose a model in which active centromeres are maintained by CENH3-enriched CentM168 arrays, while non-active pericentrometric domains are buffered by satellite-rich flanking regions.
  • The study finds that centromeric regions are enriched in young long terminal repeat (LTR) retrotransposons, suggesting a potential role for transposable elements in shaping centromeric architecture and function.

Statistics:

  • 494.47 Mb and 415.27 Mb: the sizes of the T2T genome assemblies for Medicago truncatula Jemalong A17 and Medicago littoralis R108, respectively.
  • 99% completeness: the completeness of the genome assemblies assessed by BUSCO.
  • 2 tandem satellite repeats: the composition of the centromeres of Medicago truncatula Jemalong A17, including CentM168 and the species-specific CentM183.
  • 50-70%: the proportion of centromeric DNA composed of satellite repeats.

Sources:

  • Chinese Academy of Sciences: "Breakthrough in Legume Genomics: Complete and Accurate Genome Assemblies for Medicago"
  • FENG Jian et al. (2023). Telomere-to-telomere genome assembly of Medicago truncatula and Medicago littoralis reveals striking differences in centromere composition. BioRxiv. doi: 10.1101/2023.02.20.527577 (exact date not provided)
  • PacBio HiFi sequencing, ultra-long Oxford Nanopore reads, and Hi-C chromatin conformation capture: the methods used to construct T2T genome assemblies for Medicago truncatula Jemalong A17 and Medicago littoralis R108.

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