Phased Chromosome-level Genome and Organellar Assemblies of Castilleja foliolosa Provide Vital Resource for Orobanchaceae Genomics
Castilleja (Orobanchaceae) is a diverse, facultatively hemiparasitic plant genus characterized by a complex evolutionary history of reticulate evolution and significant taxonomic ambiguity. High-quality genomic resources have historically been limited, hindering robust macro-evolutionary and macro-ecological inquiries. Here, we present the first high-quality, phased, chromosome-level reference…
The Castilleja foliolosa species, a member of the Orobanchaceae family of predominantly parasitic plants, has long posed challenges for genomic research due to its complex evolutionary history and taxonomic ambiguity. A significant breakthrough in this field is the recent presentation of the first high-quality, phased, chromosome-level reference genome for this diploid species.
This achievement was made possible through a hybrid assembly strategy, combining long-read PacBio HiFi sequencing with Omni-C proximity ligation data to construct a highly contiguous nuclear genome assembly. This nuclear assembly, spanning around 510 megabase pairs, houses approximately 39,417 predicted genes and carries a significant repetitive landscape, covering about 66% of the genome.
The study's organellar assemblies reveal a structural complexity that adds another layer of interest to this genomic analysis. The chloroplast genome exhibits heteroplasmy, with two primary structural haplotypes in play. Simultaneously, the mitochondrial genome, a 611 kilobase pair entity, follows a circular master topology that manifests in two isomeric forms.
These organellar findings are complemented by comparative genomic analyses, which show a largely conserved chromosomal architecture when compared to the closely related species, Pedicularis cranolopha. This comparative study is punctuated by the presence of lineage-specific genes in Castilleja foliolosa, suggesting evolutionary adaptations that are unique to this species.
The functional enrichment of Castilleja-specific orthogroups identified in this study provides intriguing insights into the biological roles of these genetic elements. The consistent association observed between certain orthogroups and functions such as telomere maintenance, DNA integration, and zinc ion binding is likely attributable to the substantial repeat content within the genome.
This reference genome now serves as a robust framework for researchers to delve deeper into the genomic drivers of taxonomic diversification and adaptation within the Orobanchaceae family. By providing a definitive foundation for future comparative studies, this resource significantly expands our capacity to unravel reticulate evolutionary patterns, thereby opening new avenues for understanding the genomic evolution in the Orobanchaceae lineage of parasitic plants.
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