CRISPR/Cas-mediated editing of cis-regulatory elements for crop improvement

To improve future agricultural production, major technological advances are required to increase crop production and yield. Targeting the coding region of genes via the Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated Protein (CRISPR/Cas) system has been well established and has enabled the rapid generation of transgene-free plants, which can lead to crop improvement. The emergence of the CRISPR/Cas system has also enabled scientists to achieve cis-regulatory element (CRE) editing and, consequently, engineering endogenous critical CREs to modulate the expression of target genes. Recent genome-wide association studies have identified the domestication of natural CRE variants to regulate complex agronomic quantitative traits and have allowed for their engineering via the CRISPR/Cas system. Although engineering plant CREs can be advantageous to drive gene expression, there are still many limitations to its practical application. Here, we review the current progress in CRE editing and propose future strategies to effectively target CREs for transcriptional regulation for crop improvement.