A bidirectional promoter system (BiP) was developed for genome editing, which allows expression of Cas9 and single guide RNA (sgRNA) in opposite directions. This was developed by experts from the University of Electronic Science and Technology of China, Yangzhou University, and the University of Maryland.

CRISPR-Cas9 systems have been expressed in three ways in plants: mixed dual promoter systems, dual Pol II promoter systems, and single transcript unit systems. The new strategy, reported in the Frontiers in Plant Science, was used to express CRISPR-Cas9 in rice, where BiP was used to express Cas9 and sgRNA in opposite directions. Initially, the researchers tested the system based on double-mini 35S promoter and an Arabidopsis enhancer, which resulted in 21-53% genome editing efficiencies at two target sites in T0 stable transgenic rice plants. Then they improved the BiP system by using a rice endogenous BiP (OsBiP1), which resulted in higher expression strength and higher genome editing efficiencies (76-93%) in rice.
The results provide a proof-of-concept study of BiP application for expression two-component CRISPR-Cas9 genome editing reagents in rice.
[www.frontiersin.org]