Relationships between phenotypic plasticity and epigenetic variation in two Caribbean Acropora corals

The influence of environmental history on the performance of Acropora cervicornis corals across a spatiotemporal gradient

Environmental cues can trigger plastic changes in organism phenotype which may be maintained through environmental memory. However, the duration through which phenotypic differences persist under naturally occurring environmental variation is not yet well understood. In the present study, the influence of environmental history on phenotypic plasticity was studied using corals as model organisms. Genetic clones of Acropora cervicornis corals, previously acclimatized to different environmental conditions, were reciprocally transplanted between an anthropogenically-impacted and more isolated site. The effects of environmental history on physiology and performance were characterized across spatial and temporal gradients. Our results suggest that coral physiological variation was driven by temperature, light, conductivity, and nutrient concentrations. Additionally, coral physiology, acute thermal tolerance, and growth rates differed between sites. Within the initial months following the transplant, the influence of prior environmental conditions on physiology and stress resistance was found to outweigh that of the current environment. Yet, the influence of environmental history varied both spatially and temporally, which suggested trade-offs constraining performance. We detected an increase in overlap between the physiological niches of native and transplant corals over time, demonstrating the loss of environmental memory through acclimatization to novel conditions. In fact, differences in physiology and acute thermal tolerance driven by previous environmental conditions were largely lost after eight months following the transplant. However, the effect of the original environment was still observed in coral growth rates between eight and twelve months post-transplant. Overall, the present work highlights the dynamism of environmental memory and acclimatization across environmental variation.

Phenotypic plasticity for improved light harvesting, in tandem with methylome repatterning in reef-building corals

Acclimatization through phenotypic plasticity represents a more rapid response to environmental change than adaptation and is vital to optimize organisms' performance in different conditions. Generally, animals are less phenotypically plastic than plants, but reef-building corals exhibit plant-like properties. They are light dependent with a sessile and modular construction that facilitates rapid morphological changes within their lifetime. We induced phenotypic changes by altering light exposure in a reciprocal transplant experiment and found that coral plasticity is a colony trait emerging from comprehensive morphological and physiological changes within the colony. Plasticity in skeletal features optimized coral light harvesting and utilization and paralleled significant methylome and transcriptome modifications. Network-associated responses resulted in the identification of hub genes and clusters associated to the change in phenotype: inter-partner recognition and phagocytosis, soft tissue growth and biomineralization. Furthermore, we identified hub genes putatively involved in animal photoreception-phototransduction. These findings fundamentally advance our understanding of how reef-building corals repattern the methylome and adjust a phenotype, revealing an important role of light sensing by the coral animal to optimize photosynthetic performance of the symbionts.

Involvement of 5mC DNA demethylation via 5-aza-2'-deoxycytidine in regulating gene expression during early somatic embryo development in white spruce (Picea glauca)

DNA methylation plays a crucial role in the development of somatic embryos (SEs) through the regulation of gene expression. To examine the impact of DNA methylation on gene expression during early SE development in Picea glauca, the demethylation reagent 5-aza-dC (5-aza-2'-deoxycytidine) was employed to modify DNA methylation regions and levels during the pre-maturation stage of somatic embryogenesis. The application of 2.0 µM 5-aza-dC did not induce toxicity to SEs in early development. Following treatment, the global DNA methylation level decreased significantly on the 7th day of pre-maturation and the 1st week of maturation. Methylated DNA immunoprecipitation (MeDIP) sequencing revealed that differentially methylated regions, as analyzed through Gene Ontology (GO), were related to plant development and reproduction and that they were hypomethylated on the 3rd day but hypermethylated on the 7th day in 5-aza-dC-treated embryogenic tissues. These findings indicate that 5-aza-dC treatment positively impacts early SE development, which was inhibited following 7 d of treatment. The expression of MSH7, JMJ14, and CalS10 was associated with DNA methylation, epigenetic regulation, and somatic embryogenesis. Further analysis of methylated regions revealed that the expression profiles of MSH7, JMJ14, and CalS10 were correlated with altered DNA methylation, suggesting DNA methylation at 5 mC may play a role in controlling the expression of these genes and regulating the early development of SEs in P. glauca. This study offers new insights into the regulation of somatic embryogenesis in conifers.