Transcriptomic analysis of the effects of reproduction on immunity in the clam Meretrix petechialisn during the breeding season

Immune defense and reproduction are both physiologically demanding processes, therefore the trade-off is expected between them in breeding season. Although this balance strategy has been extensively studied in many species, it remains rare in the mollusc. Moreover, summer mortality of marine bivalve often occurs during breeding season and reproduction is suspected to play a significant role for the mass death. To address if spawning affects immunity to cause clam death, we performed transcriptome and gene expression analyses on the hepatopancreas of clam Meretrix petechialis at pre-/post-spawning. DEGs enrichment analysis revealed important immune signaling pathways and key genes changed before and after spawning. The results showed females up-regulated genes involved in apoptosis, TLR signal pathway and heat shock, whereas males down-regulated complement-related genes after spawning. Additionally, under vibrio challenged, the changes of four immune-related DEGs showed both genders up-regulate their immunocompetence more drastically to against pathogen infection after spawning. Our study provides a new insight into the understanding of molecular mechanisms underlying reproduction-influenced immune differences in M. petechialis and offers some clues to explain the possible reason for clam summer mortality.

免疫防御与繁殖均为生理高消耗过程，因此繁殖季节中二者被认为存在进化权衡。尽管该平衡策略已在诸多物种中得到广泛研究，但在软体动物中相关报道仍较为匮乏。此外，海洋双壳类的夏季死亡常发生于繁殖季，且繁殖被认为是大规模死亡的重要诱因之一。为明确产卵是否通过影响免疫功能进而导致文蛤（Meretrix petechialis）死亡，本研究对其产卵前后的肝胰腺（hepatopancreas）开展了转录组与基因表达分析。差异表达基因（Differentially Expressed Genes, DEGs）富集分析显示，产卵前后存在关键免疫信号通路与核心基因的显著表达变化。结果表明，产卵后雌性个体上调了细胞凋亡（apoptosis）、Toll样受体（Toll-like Receptor, TLR）信号通路及热休克（heat shock）相关基因的表达，而雄性个体则下调了补体相关基因的表达。此外，在弧菌（Vibrio）攻毒实验中，4个免疫相关差异表达基因的表达变化显示，产卵后雌雄个体均显著增强免疫能力以抵御病原体感染。本研究为解析文蛤繁殖过程中免疫差异的分子机制提供了全新视角，并为解释文蛤夏季大规模死亡的潜在成因提供了若干线索。