ADAR-editing in mollusc species: in between physiology and antiviral responses

In the complexity of understanding the functional effects of Adenosine Deaminases Acting on RNA (ADAR) mediated RNA editing in organism biology, this thesis aims to provide an accurate description of the Mollusca ADAR1 role during viral infections and in normal physiology. In the first chapter, we provided a general introduction to the current knowledge about the role of ADAR-mediated RNA editing in physiological processes, immune response, and development across species. We also discussed the impact of ADAR-mediated RNA editing on viral evolution and antiviral mechanisms, concluding with possible applications of this knowledge in aquaculture. In the second chapter, starting from the investigation of Crassostrea gigas ADARs expression levels during viral infection, the gene CgADAR1v was identified as the most responsive. The recombinant CgADAR1v protein was produced, and its activity was tested with two different enzymatic assays. This chapter then explored the host hyper-editing profile during viral infection in bivalves, focusing attention on the putative differences between infected and non-infected samples. Finally, the limitations in tracing RNA editing sites in non-model organisms were discussed. In the third chapter, we described the transcriptional architecture of OsHV-1 and HaHV-1, unveiling how the different transcriptional strategies of the two Malacoherpesviridae could represent a way to escape from the host's innate immune system defense. Moreover, in the second article of this section, we further improved the description of the OsHV-1 transcriptional architecture. Then, we traced the RNA editing sites as both hyper-editing and single sites during an OsHV-1 infection time course in Scapharca broughtonii, investigating the possible effect of ADAR activity on viral RNA transcription. In the fourth chapter, the difficulties of tracing RNA editing sites using only RNA-seq data and the advances in understanding the possible role of ADAR proteins in mollusk physiology were presented. This chapter also included a meta-analysis of transcriptome data to understand the expression and functional implications of ADAR genes in the scallop Chlamys farreri. Analysis of the scallop ADAR genes in various tissues and developmental stages revealed their diverse expression patterns, especially in early development. Moreover, the study contributed to elucidating the impact of ADAR-mediated RNA on proteome diversification and development in bivalve mollusks. Finally, all the results were discussed in the fifth and final chapter, which also described the future perspectives that could help to elucidate the role of ADAR protein in the light of evolution and host-virus interaction in mollusks.