Abstract: Grain size is an important agronomic trait that largely determines grain yield in rice (Oryza sativa L.). The genes encoding the Growth Regulating Factors (GRFs) and G-proteins are major regulators for grain length regulation, but how these pathways are coordinated in plants remains elusive. Here, we described OsPLATZ1 as a transcriptional activator, a member of the Plant AT-rich sequence- and Zinc-binding family proteins in rice that positively regulates grain length. OsPLATZ1 interacted with multiple GRFs, and the OsPLATZ1-OsGRF4 complex bound to regulatory regions in the promoter of the G-protein gene DENSE AND ERECT PANICLE1 (DEP1) to enhance its expression, thereby regulating grain length. We used gene editing to modify the OsPLATZ1 promoter regulatory region and obtained mutant lines with downregulated or upregulated OsPLATZ1 expression depending on the type of editing event. One of these mutant lines had changes in multiple agronomic traits and improved grain yield and grain appearance quality. Our findings reveal a new regulatory module in which OsPLATZ1 connects the GRFs and G-protein signaling pathways to regulate grain length and suggest that finely modulating OsPLATZ1 activity might be a promising molecular breeding approach.

Key words: G‐protein, grain length, GRF, PLATZ, rice