pBcl-2 inhibition leads to the loss of higher thermal resilience
in preconditioned corals
Previous experiments focused on the correlation of gene expression
differences with preconditioning or acclimatization (Bay & Palumbi,
2015; Bellantuono et al., 2012; Palumbi et al., 2014), but deeper
insight into mechanisms of such processes is missing. Here, we
investigated whether higher pro-survival gene expression prevents coral
from bleaching, by inhibiting the effect of pBcl-2 in PC corals. If the
acquired higher thermotolerance is caused by the pro-survival shift in
PCD pathway, inhibition of pBcl-2 function should result in the loss of
the beneficial phenotype. Venetoclax is a BH3 mimetic small molecule
that binds to Bcl-2 protein binding domain, blocking its molecular
function (Souers et al., 2013). Six PC and NPC corals were exposed to
acute heat stress (32ºC) and simultaneously treated with 1μM venetoclax
or with DMSO (for control). Fragments were also treated with venetoclax
at ambient temperature to exclude the impact of venetoclax itself to
coral bleaching. The bleaching ratio was assessed via confocal
microscopy at the beginning of the experiment and after 5 days of heat
stress. Control samples showed no effect of venetoclax to bleaching rate
at ambient temperature, but we observed significant differences in the
phenotype of corals treated and not treated with venetoclax under heat
stress (Fig. 4, S3). After the application of venetoclax, the beneficial
phenotype was completely lost, and PC corals bleached at the same rate
as NPC corals (multi-way ANOVA microscopy_signal~ time
* conditioning * treatment; $conditioning : treatment -
p(ven-) = 0.000, p(ven+) = 0.464). Our
data show for the first time the direct functional involvement of PCD
genes in coral thermal tolerance and preconditioning.