5.1.2. Transient Expression

Another delivery strategy that can be employed to obtain transgene-free edited plant is the CRISPR transient expression system. In this technique, the screening of mutants using selectable markers (antibiotic/herbicide) is omitted to regenerate the edited progeny without the incorporation of foreign genes into the plant genome. In 2016, Zhang and co-workers successfully executed this strategy for the first time in wheat to obtain transgene-free plants [148]. Furthermore, DNA base editors such as adenine and cytidine base editors have also been transferred by the transient expression approach for attaining DNA-free base substitutions [149,150]. *Agrobacterium*-mediated transformation-based transient expression has also been successfully developed in tobacco [142], and protoplast transformation-based transgenes-free expression can also be achieved in tobacco and potato protoplasts [151,152].
