Full-length transcriptome assembly of black amur bream (Megalobrama terminalis) as a reference resource.

Background: The genus Megalobrama holds significant economic value in China, with M. terminalis (Black Amur bream) ranking second in production within this group. However, lacking comprehensive genomic and transcriptomic data has impeded research progress. This study aims to fill this gap through an extensive transcriptomic analysis of M. terminalis.

Methods and results: We utilized PacBio Isoform Sequencing to generate 558,998 subreads, totaling 45.52 Gb, which yielded 22,141 transcripts after rigorous filtering and clustering. Complementary Illumina short-read sequencing corrected 967,114 errors across these transcripts. Our analysis identified 12,426 non-redundant isoforms, with 11,872 annotated in various databases. Functional annotation indicated 11,841 isoforms matched entries in the NCBI non-redundant protein sequences database. Gene Ontology analysis categorized 10,593 isoforms, revealing strong associations with cellular processes and binding functions. Additionally, 8203 isoforms were mapped to pathways in the Kyoto Encyclopedia of Genes and Genomes, highlighting significant involvement in immune system processes and complement cascades. We notably identified key immune molecules such as alpha-2-macroglobulin and complement component 3, each with multiple isoforms, underscoring their potential roles in the immune response. Our analysis also uncovered 853 alternative splicing events, predominantly involving retained introns, along with 672 transcription factors and 426 long non-coding RNAs.

Conclusions: The high-quality reference transcriptome generated in this study provides a valuable resource for comparative genomic studies within the Megalobrama genus, supporting future research to enhance aquaculture stocks.