Sequencing and Annotation
The six cDNA libraries of liver tissues were sequenced separately using the Illumina novaseq 6000 sequencing platform. In total, we obtained 311,985,890 clean reads (99.55%) and 46.49 Gb clean data (98.90%), and in all six pools, Q30>95%. A total of 28,186 genes were generated after all the clean reads were assembled with the average length and N50 length was 2,161 bp, and 2,963 bp, respectively. These results reflect the high quality of the de novo transcriptome assembly (Table 1). After screening, 21,255 (75.41%) genes were annotated into four databases, including Nr (21,145, 75.02%), Swissprot (17603, 62.45%), KOG (14,376, 51.00%), and KEGG (14,565, 51.67%) (Fig. 1). Through Nr databases annotation, rice flower carp has high homology with Cyprinus carp (7,749, 36.70%), the following is Carassius auratus (3,304, 15.64%), and Sinocyclocheilus rhinocerous (2,358, 11.15%) (Table 2).
And a total of 328,548,250 raw reads were obtained from six cDNA libraries of whole-brain tissues. After filtering, 156,148,664 clean reads (99.54%) and 171,066,936 clean reads (99.64%) were obtained in the max group and min group, respectively. All sequencing results were submitted to NCBI. Using the Trinity assembly program, we generated a total of 50,373 genes, with an average length of 1,708 bp, N50 length of 2,523 bp, 43,726 genes greater than 500 bp, and 28,857 genes greater than 1,000 bp (Table 3). The annotation of these genes using the Swissprot, Nr, KEGG, and KOG databases resulted in 23,409, 31,196, 20,152, and 18,689 genes annotations, respectively (Fig. 2). Through Nr databases annotation, rice flower carp has high homology with Cyprinus carp (7,749, 21.99%), the following is Carassius auratus (3,304, 9.40%) (Table 2).
Analysis of DEGs
A total of 880 DEGs (different expression genes) were identified in liver tissues between the two groups. Of these, 495 DEGs were upregulated and 385 DEGs were downregulated (Fig. 3a). And 2,223 DEGs were identified in brain tissues between the two groups, 1,432 DEGs were upregulated and 791 DEGs were downregulated (Fig. 3b). One hundred and twenty-three genes have been found that differentially expressed in the two organs (Fig. 3c), including myosin regulatory light chain 2 (MYL2), myosin regulatory light chain 4 (MYL4), cAMP-response element binding protein (CREB), signal transducer and activator of transcription 1 (STAT1), Myosin Heavy Chain 4 (MHY4). Some genes that are related to the brain-pituitary-liver axis were identified, such as growth hormone receptor (GHR), somatostatin-2 (SST2), somatostatin-1a (SST1A), insulin like growth factor binding protein 2 (IGFBP2A), neuropeptide y (NPY), and insulin like growth factor 2 (IGF2). These DEGs potentially influenced the growth of rice flower carp.
GO/KEGG enrichment analysis of DEGs
GO enrichment and KEGG pathway enrichment analyses were performed using the corresponding annotations of the DEGs to understand the functional relevance of the DEGs. A total of 55 level 2 GO terms and 59 level 2 GO terms were obtained in liver tissues and brain tissues, respectively (Fig. 4). In the liver tissues, most DEGs were mainly classified into the cellular process (441 DEGs), single-organism process (427 DEGs), cell part (402 DEGs), cell (402 DEGs), and binding (390 DEGs) (Fig. 4a). In the brain tissues, most DEGs were mainly classified into the cellular process (869 DEGs), single-organism process (856 DEGs), binding (809 DEGs), cell part (804 DEGs), cell (803 DEGs), and organelle (733 DEGs) (Fig. 4b).
Differentially expressed genes were mapped to 290 pathways and 303 pathways in the KEGG database for the liver tissues and brain tissues, respectively. Twenty-seven KEGG pathways were significant from 290 KEGG pathways in total for liver tissues (P<0.05), Fig. 5a are showing the top 20 KEGG enrichment of differentially expressed genes. And 72 KEGG pathways were significant from 303 KEGG pathways in total for brain tissues (P<0.05), the top 20 of KEGG enrichment of differentially expressed genes are shown in Fig. 5b. Through significant pathway enrichment analysis, some pathways that may affect growth were enriched in liver tissues, such as PPAR signaling pathway (18 DEGs) and Glycolysis / Gluconeogenesis (18 DEGs).
Validation of RNA-Seq profiles by qRT-PCR
To validate the gene expression from RNA-seq data, twelve and eight genes were selected from liver and brain tissues, respectively, for qRT-PCR. Melting curve analysis revealed a single product for all tested genes. The high correlation between the expression of these genes in RNA-seq and qRT-PCR indicated that the transcriptome information was reliable (Fig 6).