dCas-Based Tools to Visualize Chromatin or Modify Epigenetic Marks at Specific Plant Genomic Loci.

Development of locus-specific approaches targeting precise regions on chromatin, for locus/transcription visualization or transcription/epigenetic marks editing, is a critical challenge in functional genetics and epigenetics. Systems engineered from the clustered regularly interspaced short palindromic repeats (CRISPR) and its associated endonuclease (Cas) operate through DNA sequence-specific recognition by so-called guide RNAs, which provides high flexibility and modularity for precise chromatin visualization or edition. Here, we provide an overview of the CRISPR/Cas-derived tools developed for visualization of chromatin loci in live imaging or for effective modification of gene expression. These tools make use of effector modules that combine activators, repressors, and epigenetic modifiers with a deactivated Cas protein (dCas). We present how their use in plants brought advances in visualizing or manipulating the expression of loci involved in agronomically interesting traits such as flowering time and response to drought or heat. We also discuss the limitations and future improvements of the dCas-related technologies, such as more compact and combinatorial systems, spatiotemporal targeting for fine-tuning of gene expression, and live visualization of chromatin dynamics.