Hardy Reef of Australia's Great Barrier Reef
Australia’s Great Barrier Reef (GBR) is the world's largest coral reef system. On Australia’s north-east coast it contains the 400 types of coral, 1,500 species of fish and 4,000 types of mollusc to throw some impressive numbers at you. Also impressive is the reef system is the only living thing that is visible from space. The GBR is under numerous natural pressures, including tropical storms and the resultant large influxes of freshwater, outbreaks of predatory starfish like the Crown-of-Thorns, and the El Niño Southern Oscillation (ENSO). It is also subjected to the anthropogenic (resulting from the influence of human beings) stressors like the associated changes with climate change like rising sea water temperatures and ocean acidification, over-fishing, shipping and coastal development including nutrients and pesticides input from coastal farms and cities.
A single warming event spanning a 9-month period between March and November of 2016 resulted in the loss of 29% of the reefs and it is now estimated that more than half of the corals in the GBR are now dead.What can be done? If we all reduce carbon emissions, nations adhere to their goals and we step up our game it could go a very long way. However, it does not seem like the odds are in our favor.
Corals have shown to be adaptable. A study from April this year published in PLOS Genetics used population genomics, biophysical modeling, and evolutionary simulations to predict future adaptation of the common coral Acropora millepora on the GBR. Their genetic and biophysical models indicated the migration rates of genetic alleles associated with thermal adaptation and the resulting genetic variation could be sufficient to facilitate the spread of heat-tolerant alleles to higher latitudes as the climate warms. Unfortunately, it was hypothesized that this genetic adaptation would be gradual, over 20-50 coral generations or 100-250 years, likely too slow to save the reefs.
Well then where else can we look for answers? Recently, a group of Standford scientists and their colleagues employed the revolutionary tool, Crispr/Cas9, in a proof-of-principle study to modify the genes in coral. They were successful, suggesting that this tool could possibly aid in the conservation efforts.
What the heck is Crispr/Cas9? Basically, it is a gene editing system. CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats, first discovered in archaea, later in bacteria, is part of the bacterial immune system (For review of Crispr see the following site https://ghr.nlm.nih.gov/primer/genomicresearch/genomeediting). Essentially, Crispr/Cas9 can target specific stretches of DNA and edit said stretches. Bringing it back to coral now.
Published in Proceedings of the National Academy of Sciences researchers usedCRISPR/Cas9 to induce specific mutations in the cells of the common coral Acropora millepora of the GBR. The primary investigator was Phillip Cleves, PhD, a postdoctoral scholar at Stanford, a geneticist with the goal to delineate gene function in animals.
“Up until now, there hasn’t been a way to ask whether a gene whose expression correlates with coral survival actually plays a causative role,” Cleves said. “There’s been no method to modify genes in coral and then ask what the consequences are.”
Cleves and his colleagues knocked out three genes in fertilized A. milleporaeggs: one gene which encodes for a green fluorescent protein, one red fluorescent protein and the third encoding for fibroblast growth factor (protein associated with coral colonization). The two fluorescent proteins were simply to provide the visual proof that CRISPR/Cas9’s editing knock out was successful. Theoretically, if the knock out was successful, then the mutants would no longer fluoresce red or green. The corals still glowed, but not quite as brightly, and as it turns out there are multiple copies of red and green fluorescent-protein genes. For the third gene, FGF 1a, which only has one copy, there was success. FGF production stopped in some embryos. Although, the study produced some unexpected results, it did produce interesting information. Cleves said it is not the goal to create super corals to save the oceans, “Right now, what we really want to do is figure out the basic mechanisms of how coral works and use that to inform conservation efforts in the future,” he said. “Maybe there are natural gene variants in coral that bolster their ability to survive in warmer waters; we’d want to know that.”
Now the proof-of-principal study has been completed, Cleves and others are beginning to study the ecologically relevant genes.
For the Standford University Press release of this research please see
http://med.stanford.edu/news/all-news/2018/04/crispr-used-to-genetically-edit-coral.html
