Large structural variations in the haplotype-resolved African cassava genome

Area of Science:

• Genomics
• Plant Science
• Agricultural Biotechnology

Background:

• Cassava (Manihot esculenta) is a critical global food security crop with a highly heterozygous genome.
• Traditional genome assemblies oversimplify heterozygous regions, hindering detailed genetic analysis.
• Clonal propagation preserves genetic variations, including large structural variants, between haplotypes.

Purpose of the Study:

• To generate a high-resolution, phased genome assembly for cassava, resolving individual haplotypes.
• To identify and characterize haplotype-specific structural variations within the cassava genome.
• To facilitate research into heterozygosity, structural variation, and allele-specific expression in cassava for agricultural improvement.

Main Methods:

• Utilized a combination of Pacific Biosciences (PacBio), Illumina, and Hi-C sequencing technologies.
• Employed FALCON and FALCON-Phase for genome assembly and haplotype phasing, with Hi-C for scaffolding.
• Mapped RNA-sequencing data from multiple tissue types to the phased assembly for gene expression analysis.

Main Results:

• Successfully resolved both haplotypes of the TME7 cassava line genome.
• Discovered over 5000 large, haplotype-specific structural variants (>8 Mb total), including extensive insertions and deletions.
• Integrated gene expression data into a web-based interface for community access.

Conclusions:

• The phased cassava genome assemblies provide an unprecedented resource for studying structural variation and its impact on gene expression.
• This work enhances our understanding of cassava genetics, domestication, and the genetic basis of important agricultural traits.
• The accessible data platform will empower the plant science community to explore complex genomic features in cassava.