Comparative transcriptomic analysis of gill and gonad from Mytilus under antibiotics treatment followed by different bacteria challenge

Mytilus can survive in heavily anthropized coastal waters despite being constantly surrounded by abundant microorganisms, indicating an environmental adaptation and therefore an important research significance for this species. However, there is a qualitative and quantitative lack of knowledge of the molecular mechanisms involved in the physiology and immune response of Mytilus tissues, especially in tissues other than hemocytes. For filling this gap, we have studied the transcriptome of gill and gonad of M. coruscus exposed to distinct stimuli, including antibiotics pretreatment and subsequent different bacteria challenges at two time points. A total of 36 cDNA libraries were sequenced and 245.01 Gb clean data was acquired with an average of 5.91 GB and Q30 > 94% for each library. The filtered high-quality reads were assembled into 91,850 transcripts, which after clustering resulted in 59,206 unigenes. Overall, 19,783 differentially expressed genes (DEGs) were detected from the pair-wise comparisons among the gill samples, and 12,655 DEGs among the gonad samples. Comparing with the gonad, the gill showed strong immune-related responses towards bacteria challenge, with abundant immune-related signaling pathway being disturbed, highlighting the important roles of gill in mussel immune system and the tissue specificity of mussel immune responses. The gonad showed that the DEGs induced by bacteria were mainly enriched in regulatory pathways related to cell growth and proliferation. In addition, both gill and gonad presented rapid activation towards Micrococcus luteus infection comparing with that of Vibrio parahemolyticus, indicating a more sensitivity of mussel to Gram-positive bacteria. Our data revealed different immune responses in different mussel tissues under different bacteria challenges, and thus provided clues for exploring the mechanism of mussel immune system.