Abstract
Climate change predictions suggest that sea surface temperatures will continue to increase in the coming years. Ocean warming threatens coral reefs as it can induce corals to expel the symbiotic algae that coral depend on for health and survival, typically referred to as coral bleaching. Due to the genotype-specific nature of the bleaching response, understanding the impact of genotypes on corals during thermal stress is crucial. Additionally, despite efforts to explore the transcriptomic response to heat stress, many genes associated with the thermal stress response remain unannotated due to limited gene annotation resources. These unannotated genes, termed “dark genes,” could be essential for improving our understanding of bleaching mechanisms.The objective of this study is to understand dark gene variation across genotypes in Galaxea fascicularis under thermal stress and identify important “dark gene” candidates for further annotation. An 8-day thermal stress experiment was conducted to stimulate bleaching across three different genotypes and samples were collected for bulk RNA-sequencing to obtain full gene expression profiles. Proportions of “dark genes” differentially expressed during thermal stress between and within each genotype were compared to determine the genotype-specific reaction and similarities during heat stress. Out of the 2,927 differentially expressed dark genes, four candidate “dark genes” were identified based on significant upregulation that warrant further functional analysis. These results could be fundamental to the thermal stress response and further increase our understanding of bleaching mechanisms.