Telomere-to-telomere gap-free genome assembly of the endangered Yangtze finless porpoise and East Asian finless porpoise.

Background: The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis, YFP) and the East Asian finless porpoise (Neophocaena asiaeorientalis sunameri, EFP) are 2 subspecies of the narrow-ridged finless porpoise that live in freshwater and saltwater, respectively. The main objective of this study was to provide contiguous chromosome-level genome assemblies for YFP and EFP.

Results: Here, we generated and upgraded the genomes of YFP and EFP at the telomere-to-telomere level through the integration of PacBio HiFi long reads, ultra-long ONT reads, and Hi-C sequencing data with a total size of 2.48 Gb and 2.50 Gb, respectively. The scaffold N50 of 2 genomes was 125.12 Mb (YFP) and 128 Mb (EFP) with 1 contig for 1 chromosome. The telomere repeat and centromere position were clearly identified in both YFP and EFP genomes. In total, 5,480 newfound genes were detected in the YFP genome, including 56 genes located in the newly identified centromere regions. Additionally, synteny blocks, structural similarities, phylogenetic relationships, gene family expansion, and inference of selection were studied in connection with the genomes of other related mammals.

Conclusions: Our research findings provide evidence for the gradual adaptation of EFP in a marine environment and the potential sensitivity of YFP to genetic damage. Compared to the 34 cetacean genomes sourced from public databases, the 2 new assemblies demonstrate superior continuity with the longest contig N50 and scaffold N50 values, as well as the lowest number of contigs. The improvement of telomere-to-telomere gap-free reference genome resources supports conservation genetics and population management for finless porpoises.