Reduced thermal tolerance in a coral carrying CRISPR-induced mutations in the gene for a heat-shock transcription factor

Abstract

Reef-building corals are keystone species that are threatened by anthropogenic stresses including climate change. To investigate corals’ responses to stress and other aspects of their biology, numerous genomic and transcriptomic studies have been performed, generating many hypotheses about the roles of particular genes and molecular pathways. However, it has not generally been possible to test these hypotheses rigorously because of the lack of genetic tools for corals or closely related cnidarians. CRISPR technology seems likely to alleviate this problem. Indeed, we show here that microinjection of single-guide RNA/Cas9 ribonucleoprotein complexes into fertilized eggs of the coralAcropora milleporacan produce a sufficiently high frequency of mutations to detect a clear phenotype in the injected generation. Based in part on experiments in a sea-anemone model system, we targeted the gene encoding Heat Shock Transcription Factor 1 (HSF1) and obtained larvae in which >90% of the gene copies were mutant. The mutant larvae survived well at 27 °C but died rapidly at 34 °C, a temperature that did not produce detectable mortality over the duration of the experiment in wild-type (WT) larvae or larvae injected with Cas9 alone. We conclude that HSF1 function (presumably its induction of genes in response to heat stress) plays an important protective role in corals. More broadly, we conclude that CRISPR mutagenesis in corals should allow wide-ranging and rigorous tests of gene function in both larval and adult corals.

Multi-omic characterization of the thermal stress phenome in the stony coralMontipora capitata

“…Significant effort will be needed to modify this polygenic trait in coral holobionts to boost resilience in the long term. Nonetheless, we have identified a number of novel genes that are promising candidates for functional analysis using the recently developed CRISPR/Cas9 tools for corals (20,56,57). It is important to remember that the algal symbionts of corals play a key role in holobiont biology and stress response vis-à-vis symbiotic nutrient cycling (58).…”

Insights into coral bleaching under heat stress from analysis of gene expression in a sea anemone model system

“…We used the small sea anemone Aiptasia (sensu Exaiptasia pallida), a model system with great advantages for study of many aspects of cnidarian-dinoflagellate symbiosis (47)(48)(49), including the long-term viability of fully aposymbiotic animals (43,50,51). The results obtained suggest hypotheses about the molecular and cellular mechanisms of heat-stress response and bleaching that should be testable using the geneknockdown and gene-knockout methods that are becoming available for symbiotic cnidarians (52)(53)(54).…”

“…Resolution of these questions is likely to come only when the rates of bleaching can be evaluated in animals in which the genes encoding NFκB and/or others of this early up-regulated set have been inactivated. Fortunately, such experiments should soon be possible using the recently developed methods for morpholinobased gene knockdown (52) and CRISPR-based gene knockout (53,54)…”

Coral reefs in the Anthropocene Ocean: novel insights from skeletal proxies of climate change, impacts, and resilience

“…2) To bridge the decades of inescapable warming in the near future by protecting coral biodiversity through active restoration efforts aimed at preserving endangered coral species, actively propagating thermally tolerant individuals, and fostering local community interest and involvement in mutually beneficial reef preservation These efforts will only be effective in so far as anthropogenic warming is curbed substantially in the next century, however coral reef optimists have already identified these focuses and efforts are being made in both directions. has not yet been put to expansive use (Cleves et al 2020). While a coral genomics tool for identifying tolerant corals may become viable in the future, current efforts focus on identifying tolerant corals post stress, either via direct stress testing or after natural marine heatwaves.…”