Editorial: Insights in genome editing tools and mechanisms: 2022.

Genome editing technologies are important tools for studying the specific functions of individual genes or modulating the expression of important genes in organisms for biological research. CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR associated) is the prokaryotic adaptive immune system that protects hosts from invading viruses and plasmids. CRISPR/Cas9 systems are the most frequently used type of genome editing tool, which is composed of the Cas9 nuclease and the guide RNA which directs Cas9 to the target DNA site by sequence complementarity. In natural systems, guide RNAs are composed of two separate RNA molecules, the CRISPR RNA (crRNA) and the transactivating crRNA (tracrRNA), which are commonly artificially fused together to yield a single guide RNA for genome editing (Jinek et al., 2012). In addition to CRISPR/Cas9, a variety of other CRISPR-Cas systems, such as CRISPR/Cas12a (Cpf1), have been developed to overcome the difficulties of genome editing at different loci in different organisms. Recently, several new CRISPR/Cas systems have been identified and employed for genome editing, some of which are bacteriophage origin (Al-Shayeb et al., 2022). In addition, efforts have continuously been made to optimize genome editing efficiency by different CRISPR/ Cas systems belonging to all six known types. Furthermore, CRISPR/Cas9 systems have been optimized for reducing their toxicity and for boosting knock-in efficiency in genome editing of primary human cells by using long single-stranded DNA homology-directed repair templates with short regions of double-stranded DNA containing Cas9 target sequences on both ends (Shy et al., 2023). This Research Topic is aimed to further explore the application of CRISPR/Cas genome editing tools in more biological systems and it includes four research articles. Three articles are under the category of Original Research, and one belongs to the Brief Research Report. Peanut (Arachis hypogaea L.) seeds are the source of our daily edible oil and are rich in monounsaturated oleic acid and polyunsaturated linoleic acid. Fatty Acid Desaturase 2 (FAD2) catalyzes the conversion of oleic acid to linoleic acid. Compared with linoleic acid, oleic acid has better oxidative stability and health benefits, but increasing oleic acid content by knocking out the FAD2 gene can lead to poor plant stress tolerance. The RY repeat element and 2S seed protein motif cis-regulatory elements in the 5′UTR of FAD2 genes have been suggested to have enhancer activity. Neelakandan et al. targeted these two cisregulatory elements of the FAD2 gene promoter by CRISPR/Cas9 to downregulate the expression levels of two homologous FAD2 genes in seed while maintaining normal OPEN ACCESS