Gene body methylation is involved in coarse genome-wide adjustment of gene expression during acclimatization

Despite widespread taxonomic representation, the function of gene body methylation (GBM) remains uncertain. One hypothesis is that GBM mediates phenotypic plasticity. To investigate this hypothesis, we performed whole-genome methylation and transcriptome profiling on reciprocally transplanted colony fragments of the reef-building coral Acropora millepora. GBM was only slightly affected by transplantation but these small changes correlated with coral fitness in the new environment. Specifically, for transplanted corals, similarity in GBM patterns to native corals positively correlated with growth rate, as well as carbohydrate, protein, lipid and endosymbiont content. Between populations, elevated GBM positively correlated with transcription, supporting previous findings that GBM is associated with stable and active transcription. Contrary to expectations however, changes in transcription as a result of transplantation did not correlate with changes in GBM and did not predict fitness. This indicates that on physiological time scales GBM is not directly coupled to transcription, leaving open the question about the mechanism linking GBM to fitness during acclimatization.