In September 1997,the International Rice Genome Sequencing Project was launched.This initiative pooled the resources of ten nations to obtain the first complete rice genome sequence,and promoted rice research and breeding into the post-genomics era(Li et al.,2018).In 2008,an internationally coordinated project named “RICE2020” was proposed to systematically and fully characterize all rice genes,transcripts,and proteins(Zhang et al.,2008).While genes and their transcripts can be readily characterized by sequencing-and PCR-based methods,the characterization of protein dynamics including protein levels,subcellular localizations,post-transla-tional modifications,and interactions with macromolecules(e.g.,proteins,DNA,RNA,carbohydrates,and lipids)and small molecules(e.g.,metabolites and ligands)is much more challenging and usually requires antibodies that specifically recognize the protein of interest.Because it is very difficult to systematically produce reliable antibodies for the specific recognition of individual plant proteins,a common practice is to transform a tag-fused open reading frame(ORF)of a gene to the corresponding loss-of-function mutant plants.However,such an ectopically expressed tagged protein may not fully reca-pitulate the properties of the endogenous protein due to the random insertion of the transgene,even when the transgene is expressed under the endogenous gene promoter.A preferred so-lution is to genetically label the coding sequence of the gene of interest,at its in vivo locus,with a sequence encoding a fluores-cent protein tag or an affinity tag such as FLAG or HA.Such “in-locus” protein tagging,as we are naming it here,has been carried out genome-wide in yeast,Caenorhabditis elegans,fly,and mammalian cultured cells,greatly facilitating the characterization of proteins in these organisms(Jiang et al.,2018).In 2017,a Genome Tagging Project was launched in mice,aiming to label every protein using a CRISPR/Cas9-based “artificial spermatids”method(Jiang et al.,2018).Significant funding and efforts have been put into this project,which is expected to provide valuable mouse resources to accelerate biomedical research.In higher plants,in-locus tagging of proteins has been extremely challenging technically.