Gene ontology (GO) enrichment analysis
To identify molecular mechanisms involved in the polyp bail-out
response, GO enrichment analyses were conducted for up- and
downregulated DEGs. As most eriched GO terms in our results are likely
involved as general responses of corals to osmotic fluctuations, the
discussion of which is beyond the scope of this study, we paid specific
attention to biological processes and signaling pathways related to
apoptosis, ECM degradation, and cell survival, which participate
directly in polyp bail-out. Among upregulated DEGs, GO categories such
as apoptotic process , extrinsic apoptotic signaling
pathway , negative regulation of cell death , fibroblast
growth factor (FGF) receptor signaling pathway , and tumor
necrosis factor (TNF)-mediated signaling pathway were significantly
enriched at both 12 h and 24 h (p <0.05), while
enrichment of I-κB kinase/NF-κB signaling was significant at 12 h
but not at 24 h (Table 1). In addition, in our transcriptomic data we
found remarkable upregulation of eight matrix metalloproteinase
(MMP)-encoding transcripts (>10-fold expression change from
0 h to 24 h), although enrichment of the GO category proteolysiswas insignificant (p = 0.20 at 12 h and 0.14 at 24 h). Among
downregulated DEGs, no specific signaling pathway or
apoptosis/proteolysis-related GO category showed significant enrichment.