Precise genome editing by systems like CRISPR Cas9 needs high-efficiency
homology-directed repair (HDR). Various techniques have been developed to
improve HDR but with limited success. Thus, scientists from King Abdullah
University of Science and Technology in Saudi Arabia fused Cas9 endonuclease
and the Agrobacterium VirD2 relaxase (Cas9-VirD2) to facilitate HDR. The
results of their study are published in Nature.



The resulting protein exhibits the functions of Cas9, which causes targeted
and specific DNA double-strand breaks, and the VirD2 relaxase, which brings
the repair template close to the double strand breaks, to facilitate HDR.
The Cas9-VirD2 system was tested and worked well for precise ACETOLACTATE
SYNTHASE (OsALS) allele modification to generate herbicide resistant rice
plants, CAROTENOID CLEAVAGE DIOXYGENASE-7 (OsCCD7) to engineer plant
architecture, and generate in-frame fusions with the HA epitope at HISTONE
DEACETYLASE (OsHDT) locus.

Based on the results, the Cas9-VirD2 system can be used to improve the vital
characteristics of crops. It also opens new possibilities for precision
genome engineering of eukaryotic species.



[www.nature.com]