Transcriptome assembly and identification of genes and SNPs associated with growth traits in largemouth bass (Micropterus salmoides).

Growth is one of the most crucial economic traits of all aquaculture species, but the molecular mechanisms involved in growth of largemouth bass (Micropterus salmoides) are poorly understood. The objective of this study was to screen growth-related genes of M. salmoides by RNA sequencing and identify growth-related single-nucleotide polymorphism (SNP) markers through a growth association study. The muscle transcriptomes of fast- and slow-growing largemouth bass were obtained using the RNA-Seq technique. A total of 54,058,178 and 54,742,444 qualified Illumina read pairs were obtained for the fast-growing and slow-growing groups, respectively, giving rise to 4,865,236,020 and 4,926,819,960 total clean bases, respectively. Gene expression profiling showed that 3,530 unigenes were differentially expressed between the fast-growing and slow-growing phenotypes (false discovery rate ≤0.001, the absolute value of log2 (fold change) ≥1), including 1,441 up-regulated and 2,889 down-regulated unigenes in the fast-growing largemouth bass. Analysis of these genes revealed that several signalling pathways, including the growth hormone-insulin-like growth factor 1 axis and signalling pathway, the glycolysis pathway, and the myostatin/transforming growth factor beta signalling pathway, as well as heat shock protein, cytoskeleton, and myofibril component genes might be associated with muscle growth. From these genes, 10 genes with putative SNPs were selected, and 17 SNPs were genotyped successfully. Marker-trait analysis in 340 individuals of Youlu No. 1 largemouth bass revealed three SNPs associated with growth in key genes (phosphoenolpyruvate carboxykinase 1, FOXO3b, and heat shock protein beta-1). This research provides information about key genes and SNPs related to growth, providing new clues to understanding the molecular basis of largemouth bass growth.