Genomic comparison of the temperate coralAstrangia poculatawith tropical corals yields insights into winter quiescence, innate immunity, and sexual reproduction

Abstract

AbstractFacultatively symbiotic corals provide important experimental models to explore the establishment, maintenance, and breakdown of the mutualism between corals and members of the algal family Symbiodiniaceae. The temperate coralAstrangia poculatais one such model as it is not only facultatively symbiotic, but also occurs across a broad temperature and latitudinal gradient. Here, we report thede novochromosome-scale assembly and annotation of theA. poculatagenome. Though widespread segmental/tandem duplications of genomic regions were detected, we did not find strong evidence of a whole genome duplication (WGD) event. Comparison of the gene arrangement betweenA. poculataand the tropical coralAcropora milleporarevealed 56.38% of the orthologous genes were conserved in syntenic blocks despite ∼415 million years of divergence. Gene families related to sperm hyperactivation and innate immunity, including lectins, were found to contain more genes inA. milleporarelative toA. poculata. Sperm hyperactivation inA. milleporais expected given the extreme requirements of gamete competition during mass spawning events in tropical corals, while lectins are important in the establishment of coral-algal symbiosis. By contrast, gene families involved in sleep promotion, feeding suppression, and circadian sleep/wake cycle processes were expanded inA. poculata. These expanded gene families may play a role inA. poculata’s ability to enter a dormancy-like state (“winter quiescence”) to survive freezing temperatures at the northern edges of the species’ range.