Telomere-to-telomere Genome Assembly of Equus kiang (Tibetan wild donkey).

Overview

• This research presents a complete and highly detailed genome assembly of the Tibetan wild donkey (Equus kiang) at the chromosomal level, achieved through advanced DNA sequencing technologies.
• The assembly offers significant insights into the species’ chromosomal diversity and genomic structure compared to the domestic horse, contributing valuable information for studies in evolution and genetics.

Introduction to Equus kiang and Research Objectives

• Species Background: Equus kiang, or the Tibetan wild donkey, is native to the Qinghai-Tibet Plateau and represents a unique member of the Equus genus known for its distinct chromosomal characteristics.
• Purpose: The study aimed to generate a telomere-to-telomere (complete) genome assembly to better understand the genetic and chromosomal composition of E. kiang and to facilitate comparative genomics within the Equus genus.

Methodology

• Sequencing Technologies Used:
• Illumina short reads: Provided accurate base-level information for the genome.
• PacBio HiFi long reads: Delivered long, high-fidelity sequence reads allowing comprehensive assembly of complex regions.
• Hi-C sequencing data: Used for capturing the 3D genome structure, aiding in the assembly of sequences into chromosome-level scaffolds.
• Assembly Results:
• Total genome size assembled was approximately 4.02 gigabases (Gb).
• The assembly resolved into 27 pseudochromosomes representing the chromosomal structure.
• Chromosome gap evaluation showed:
• 8 chromosomes were completely gapless (fully contiguous).
• 8 chromosomes had only one gap.
• 7 chromosomes contained 2 to 4 gaps.
• 4 chromosomes contained five or more gaps.

Quality Assessment

• BUSCO Analysis: Benchmarking Universal Single-Copy Orthologs analysis assessed the completeness of the genome assembly, with a result of 96.7% completeness, indicating a high-quality assembly suitable for further scientific investigation.

Comparative Genomics with Domestic Horse (Equus caballus)

• Chromosome Correspondence: Comparative genome collinearity analysis showed that 11 of the E. kiang chromosomes had direct one-to-one correspondence with E. caballus chromosomes, suggesting conserved synteny in these regions.
• Genomic Feature Insights: Regions near recombination breakpoints were notably enriched with tandem repeats, suggesting these repetitive sequences may play a role in chromosomal evolution and recombination events.

Significance and Future Applications

• This comprehensive genome assembly serves as a crucial resource for further research into:
• Chromosome evolution mechanisms within the Equus genus and mammals in general.
• Speciation processes by providing detailed genomic comparisons.
• The genetic basis of unique adaptations of the Tibetan wild donkey to the harsh environment of the Qinghai-Tibet Plateau.
• Broader genomic architecture studies to understand repetitive elements and their effects on genome stability and function.
• The assembly represents an important foundation for conservation genetics and evolutionary biology related to this species and equids as a whole.