Symbiont codominance is associated with reduced coral stress
We were next interested in how symbiont codominance is reflected in the
host functional profile. In addition to analyzing the effect of
codominance on its own, we were also interested in how symbionts’
codominance modifies the host response to heat stress (i.e.,
codominance:heat interaction). To better interpret the coral host
functional profiles, we used eukaryotic orthologous group (KOG) analysis
to identify broader functional categories of modulated genes and to
formally compare these results to the known profile of Acroporasp. response to various kinds of high-intensity stress (generalized
stress response, “GSR”;Dixon et al.,2020). This analysis revealed that host gene expression response
to symbiont codominance had no significant correlation with the GSR (Fig
4B), indicating that harboring codominant symbionts does not stress the
host. Instead, supporting the GO analysis results, the “translation,
ribosomal structure, and biogenesis” category was up-regulated (Fig.
4A), suggesting stimulation of cellular growth
(Giordiano
et al., 2015;Elser
et al., 2003;Bosdriez
et al., 2015;López-Maury
et al., 2008). As expected, gene expression of the
heated corals strongly correlated with the GSR (r = 0.66, p = 0.00058,
Fig. 4C), implying that the corals were stressed by the treatment.
However, delta-ranks for the heat:codominance interaction term were
negatively correlated with the GSR (r=-0.79, p=5.9e-06, fig. 4D), which
means that hosting codominant symbionts mitigated the heat stress
response.