The
CRISPR/Cas9 method is based on a natural system used by bacteria to protect
themselves from infection by viruses. When the virus inject its DNA into the
bacteria’s cell enzymes cut a piece of the viral DNA out of its helix and
integrate that into its own DNA on a specific site called CRISPR sequence. The
cell will copy that sequence into a crRNA and a tRNA. These two RNA’s bind than
onto a protein and form a complex called CAS9. CAS9 is an endonuclease, a type
of Enzyme that can cut DNA. When the matching sequence known as a guide RNA
finds its target in the viral Genome the CAS9 will start to unzip the DNA and
match it to its target RNA. If the match is completed the CAS9 will use two
tiny molecular scissors to cut the DNA. When this happens the cell try to
repair the cut but the repair process is irreversible leading to mutations that
can disable the gen. Over the past few year researcher studied the system and
realize that it could be engineered not to just cut viral DNA but any DNA
sequence at a precisely chosen location by changing the guide RNA to match the
target. To be even more precise a DNA can be added which carries the desire
sequence. Once the CAS9 made a cut the new DNA template can pair up with the
cut ends, recombining and replacing the original sequence with a new version.
In wheat, powdery mildew is one of the most destructive plant pathogens worldwide. Bread wheat is an allohexaploid, with three similar but not identical copies of most of its genes. For this reason, breeders have not managed to breed a mildew resistant plants to this day. But the CRISPR/Cas9 system could lead searcher to revolutionary results. By targeting the three called MLO sequences, which encode proteins that were shown to repress defences against powdery mildew diseases in other plants, a durable resistance to the fungal pathogens that cause powdery mildew could be created. (Wang et al., 2014)
In order to achieve the desired genome editing in the target cell the Cas9
protein and the sgRNA needs to be delivered into the nucleus of the living
cell. Those two key elements of the CRISPR/Cas9 system can
be can be expressed either from expression vectors or by
microinjected RNA and mRNA. By using the CRISPR/Cas9
approach the most common delivery method in genome
editing are the Agrobacterium-mediated transformation, the polyethylene
glycol-mediated transformation and the shotgun method. Furthermore, the
selection of the matching promoter and a codon-optimized versions of Cas9 are
very important for efficient genome editing. (Kumar and Jain, 2015)
Discussing the advantage and disadvantage of new barley known technology
is a challenging task. Fact is the CRISPR/Cas9 system is a very powerful tool
in genome editing. But as it
is the case with any new technology, the benefits of CRISPR/Cas9 are followed
by equally huge risks from potential misuse, but also unforeseen consequences. Since the DNA of a CRISPR-modified plant doesn’t interfere with a control
group, I don’t believe that the consumption of such a plant is dangerous. About what I am worried about is potential loss of biodiversity and the
missing regulation of the government worldwide which causes possible misuse.
Refrences
Kumar, V. and Jain, M. (2015). The CRISPR–Cas9 system
for plant genome editing: advances and opportunities. Journal of Experimental Botany Vol. 66: 47–57
Wang, Y., Cheng, X., Shan, Q.,
Zhang, Y., Liu, J., Gao, C. and Qiu
J.-L. (2014). Simultaneous editing of three homoeoalleles in
hexaploid bread wheat confers heritable resistance to powdery mildew. Nature Biotechnology 32:1-6
