Chromatin accessibility and heat stress gene expression in the reef-building coral, Acropora millepora

Understanding how organisms regulate gene expression to maintain homeostasis in the face of environmental changes is critical, particularly considering increasing climate stressors. While DNA methylation has dominated the literature on epigenetic control of gene expression in ecological systems, alternative epigenetic layers may provide additional insight into mechanisms of gene expression regulation. This study investigates the role of chromatin accessibility in influencing gene expression in the reef-building coral Acropora millepora, especially in response to thermal stress. We find that highly accessible regions of chromatin, or open chromatin, are predominantly located in distal intergenic regions, promoters, and introns. Genes with open promoters exhibit increased expression and reduced variability, suggesting that chromatin accessibility may influence gene expression plasticity. The baseline state of promoter accessibility is weakly correlated with the expression response to heat stress, suggesting chromatin state can influence organismal response to environmental stress. This study contributes new insights into regulatory mechanisms important for responding to acute environmental stressors. This work also establishes a foundation to investigate the interactions between chromatin accessibility, additional epigenetic layers, and how the dynamics of these interacting epigenetic layers contribute to adaptive molecular and cellular responses, which will be critical for understanding organismal resilience to ongoing environmental change.