Telomere-to-telomere genome assembly of Electrophorus electricus provides insights into the evolution of electric eels.

Background: Electric eels evolved remarkable electric organs that enable them to instantaneously discharge hundreds of volts for predation, defense, and communication. However, the absence of a high-quality reference genome has extremely constrained the studies of electric eels in various aspects.

Results: Using high-depth, multiplatform sequencing data, we successfully assembled the first telomere-to-telomere high-quality reference genome of Electrophorus electricus, which has a genome size of 833.43 Mb and comprises 26 chromosomes. Multiple evaluations, including N50 statistics (30.38 Mb), BUSCO scores (97.30%), and mapping ratio of short-insert sequencing data (99.91%), demonstrate the high contiguity and completeness of the electric eel genome assembly we obtained. Genome annotation predicted 396.63 Mb repetitive sequences and 20,992 protein-coding genes. Furthermore, evolutionary analyses indicate that Gymnotiformes, which the electric eel belongs to, has a closer relationship with Characiformes than Siluriformes and diverged from Characiformes 95.00 million years ago. Pairwise sequentially Markovian coalescent analysis found a sharply decreased trend of the population size of E. electricus over the past few hundred thousand years. Furthermore, many regulatory factors related to neurotransmitters and classical signaling pathways during embryonic development were significantly expanded, potentially contributing to the generation of high-voltage electricity.

Conclusions: This study not only provided the first high-quality telomere-to-telomere reference genome of E. electricus but also greatly enhanced our understanding of electric eels.