The draft genome of an octocoral, dendronephthya gigantea

Abstract

Coral reefs composed of stony corals are threatened by globalmarine environmental changes. However, soft coral communities of octocorallian species, appear more resilient. The genomes of several cnidarians species have been published, including from stony corals, sea anemones, and hydra. To fill the phylogenetic gap for octocoral species of cnidarians, we sequenced the octocoral, Dendronephthya gigantea, a nonsymbiotic soft coral, commonly known as the carnation coral. The D. gigantea genome size is ~276Mb. A high-quality genome assembly was constructed fromPacBio long reads (29.85 Gb with 108× coverage) and Illumina shortpaired-endreads (35.54Gbwith128×coverage) resultinginthehighestN50value (1.4Mb) reportedthus far amongcnidarian genomes. About 12%of the genome is repetitive elements and contained 28,879 predicted protein-coding genes. This gene set is composed of 94%complete BUSCOortholog benchmarkgenes,which is the second highest value amongthe cnidarians, indicating high quality.Basedon molecular phylogenetic analysis, octocoral and hexacoraldivergence timeswere estimatedat544MYA. There is a clear difference in Hox gene composition between these species: unlike hexacorals, the Antp superclass Evx genewas absent in D. gigantea.Here,we present the first genomeassembly of a nonsymbiotic octocoral,D. gigantea to aid in the comparative genomic analysis of cnidarians, including stony and soft corals, both symbiotic and nonsymbiotic. The D. gigantea genomemay also provide clues to mechanisms of differential coping between the soft and stony corals in response to scenarios of global warming.