Transcriptome Analysis to Identify Cold-Responsive Genes in Amur Carp (Cyprinus carpio haematopterus).

The adaptation of fish to low temperatures is the result of long-term evolution. Amur carp (Cyprinus carpio haematopterus) survives low temperatures (0-4°C) for six months per year. Therefore, we chose this fish as a model organism to study the mechanisms of cold-adaptive responses using high-throughput sequencing technology. This system provided an excellent model for exploring the relationship between evolutionary genomic changes and environmental adaptations. The Amur carp transcriptome was sequenced using the Illumina platform and was assembled into 163,121 cDNA contigs, with an average read length of 594 bp and an N50 length of 913 bp. A total of 162,339 coding sequences (CDSs) were identified and of 32,730 unique CDSs were annotated. Gene Ontology (GO), EuKaryotic Orthologous Groups (KOG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to classify all CDSs into different functional categories. A large number of cold-responsive genes were detected in different tissues at different temperatures. A total of 9,427 microsatellites were identified and classified, with 1952 identifying in cold-responsive genes. Based on GO enrichment analysis of the cold-induced genes, "protein localization" and "protein transport" were the most highly represented biological processes. "Circadian rhythm," "protein processing in endoplasmic reticulum," "endocytosis," "insulin signaling pathway," and "lysosome" were the most highly enriched pathways for the genes induced by cold stress. Our data greatly contribute to the common carp (C. carpio) transcriptome resource, and the identification of cold-responsive genes in different tissues at different temperatures will aid in deciphering the genetic basis of ecological and environmental adaptations in this species. Based on our results, the Amur carp has evolved special strategies to survive low temperatures, and these strategies include the system-wide or tissue-specific induction of gene expression during their six-month overwintering period.