Figure 4 Preconditioned (PC) corals treated with Bcl-2 inhibitor venetoclax lost the more thermal-resilient phenotype and bleached at the same rate as non-preconditioned (NPC) corals. A) Bleaching rate of PC and NPC corals based on calculating the symbiont: host cells signal ratio. A set of control experiments was designed to rule out the effect of venetoclax itself on coral symbiont density. Three-way ANOVA analysis with Tukey’s post hoc test (microscopy_signal ~ time * conditioning * treatment) was used to test the similarity of bleaching rate. The analysis showed a significant difference in bleaching rate between PC and NPC corals not treated with venetoclax (p <0.001) but no difference in corals treated with venetoclax (p = 0.9871) pointing to the crucial role of pBcl-2 in acclimatization and coral bleaching. Graphs show mean values with standard error bars, grey shadows along the lines represent 95% confidence level interval, * indicates a statistically significant difference, n = 5.  B) Fluorescence confocal microscopy pictures of coral fragments that underwent 5-day long heat stress without or with venetoclax. Each treatment is represented by two different corals, 0 and 5 days the same coral fragment at different timepoints captured by the live imaging technique. Host cells are visualized in green (GFP), algal cells in red (chlorophyll A), the third picture shows merged layers. The white bar represents 1mm. 
 
Figure 5