Tools of the future
March 28, 2017
By Brandi Cowen
The pace of progress can be astonishing when we slow down enough to reflect on where we’ve been, where we are, and where we’re going. Take, for instance, the rapid technological changes each of us has lived through. I have vague childhood memories of introducing my aunt to the wonders of Pac-Man on my family’s state-of-the-art Commodore 64. Fast-forward 20-odd years and I was introducing her to the much smaller, much more powerful iPad mini. Just think what I might be introducing her to in another 20 years. Our wildest imaginings will probably fall short of what two decades of innovation will accomplish.
Science, too, often seems to move at a breakneck pace. Last October, Top Crop Manager published an article exploring opportunities for researchers to use the CRISPR-Cas9 gene editing system to accelerate plant breeding. Just a few short months later, I found myself reading up on a related advancement – one that could have important implications for plant breeders.
CRISPR-Cas9 originally evolved as an immune system to protect bacteria from viral infections. In recent years, scientists discovered they could also use it to target and edit DNA, removing the genes responsible for various traits in an organism’s genetic code or adding genetic material from another organism to introduce new traits. Once the edits have achieved the desired results, researchers can remove the foreign genes, leaving them with a plant that’s not considered transgenic.
Though CRISPR-Cas9 shows promise, it’s not a perfect system for gene editing. The technique can be imprecise, leading to accidental edits in addition to the planned ones. That’s why researchers at the University of California San Francisco (UCSF) were excited to identify anti-CRISPR proteins that can deactivate CRISPR-Cas9.
The team studied almost 300 strains of Listeria bacteria and found three per cent showed proof of so-called self-targeting – strains in which a virus made its way through the bacteria’s immune system to insert its genes into the bacteria’s DNA. In order to do so, the team reasoned, these viruses must possess some sort of anti-CRISPR trait.
“Cas9 isn’t very smart,” said Joseph Bondy-Denomy, a UCSF Sandler Faculty Fellow in the department of microbiology and immunology, in a press release. “It’s not able to avoid cutting the bacterium’s own DNA if it is programmed to do so. So we looked for strains of bacteria where the CRISPR-Cas9 system ought to be targeting its own genome. The fact that the cells do not self-destruct was a clue that the whole CRISPR system was inactivated.”
The team located four anti-CRISPR proteins that interfered with the Cas9 protein’s activity in Listeria. Further research found two of those proteins – AcrllA2 and AcrllA4 – can also interfere with the ability of SpyCas9 (the protein responsible for DNA clipping) to target genes in other bacteria and even in engineered human cells. This points to both proteins as effective inhibitors of CRISPR-Cas 9 editing.
“Researchers and the public are reasonably concerned about CRISPR being so powerful that it potentially gets put to dangerous uses. These inhibitors provide a mechanism to block nefarious or out-of-control CRISPR applications,” Bondy-Denomy said. The discovery of these anti-CRISPR proteins also opens up new avenues of research, including a search for more effective CRISPR-deactivating proteins.
Whatever the future holds for CRISPR-Cas9 and other plant breeding tools yet to be imagined, you can be sure we’ll explore it in Top Crop Manager.