Transcriptome Analysis Reveals Impaired Fertility and Immunity Under Salinity Exposure in Juvenile Grass Carp

Jingjing Zhang,Jie Li,Yujie He,Zhi Wu,Xinhui Li

doi:10.3389/fmars.2021.697813

Abstract

Grass carp (Ctenopharyngodon idellus) is one of the most economically important aquaculture species and is widely cultured in China. However, its wild populations in many rivers are increasingly declining, and seawater intrusion is one of the most important threats to their survival. However, the mechanisms underlying the decline due to salinity pressure are still unknown. Here, we performed a comparative transcriptome analysis of C. idellus larvae in response to salinity exposures; a total of 481 differentially expressed genes (DEGs) were identified. These DEGs were significantly enriched in eight Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, among which steroid biosynthesis was the most important one, with the highest enrichment score. The pathway plays an important role in the development of the testes and ovary. Interestingly, all DEGs in steroid biosynthesis showed a down regulation, indicating that salinity exposure may pose damage to the fertility of C. idellus. Furthermore, three immunity-associated pathways (cytokine–cytokine receptor interaction, Toll-like receptor signaling pathway, and NOD-like receptor signaling pathway) were also significantly enriched, suggesting impaired immunity and a high risk of disease infection under salinity exposure. Overall, damage to both fertility and immunity would decrease the number of offspring and increase the risk of death due to disease infection. Our results provide a potential molecular mechanism underlying the decline of wild C. idellus populations in the Pearl River.

Highlights

Seawater intrusion is a natural phenomenon along shores
To understand the molecular mechanisms underlying the damage to grass carp caused by sea intrusion, we performed comparative transcriptome expression analyses to identify the differentially expressed genes (DEGs) between the salinity stress group and the control group
We identified a total of eight Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways with high enrichment, among which the steroid biosynthesis pathway had the highest enrichment score

Summary

Introduction

Seawater intrusion is a natural phenomenon along shores. seawater intrusion has intensified and frequently occurs downstream of rivers in recent years mainly due to global climate warming, which is accelerating the rise of sea levels (Melloul and Collin, 2006; Werner and Simmons, 2010; Werner et al, 2013). Seawater intrusion to inland river regions can increase the salinity concentrations and pose a threat to freshwater species (Nguyen et al, 2009). Its wild resource in many systems, such as the Pearl River, has declined rapidly in the past years (Fishery Statistical Yearbook of China, 2017, 2018, 2019, 2020). The decline poses a threat to the protection of biodiversity in freshwater realms and has potential negative effects on the aquaculture industry of grass carp, given that wild populations can provide excellent germplasm resources to avoid inbreeding depression (Berthelot et al, 2014; Lu and Luo, 2020). The mechanisms underlying the decline due to salinity pressure are still unknown

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Results

Conclusion