Nitrogen fertilization is essential to increase grain yield, whereas it also promotes stem and leaf elongation and makes crop plants more susceptible to lodging. It is well-known that Green Revolution is the introduction of semidwarfism into wheat and rice, which also improves the harvest index by the reduced plant height. However, the semidwarf (sd1) gene also causes the reduction of panicle branching and biomass in rice. Through genetic mapping, we identified a major QTL in rice , qDEP1, which encodes a plant specific G-protein γ-subunit and determines both panicle architecture and nitrogen growth responses. Different DEP1 alleles confer different nitrogen responses, and genetic diversity analysis suggests that DEP1 has been subjected to artificial selection during japonica rice domestication. Interestingly, dep1 plants are not only semidwarf but also have increased nitrogen-use efficiency. The DEP1 protein physically interacts with Gα (RGA1), and Gβ (RGB1) and reduced RGA1 or enhanced RGB1 activity represses nitrogen-mediated growth. Further, DEP1 could physically interact with transcriptional factors and regulate the expression of their down-stream genes.  Modulation of the G-protein signalling thus represents an important strategy to simultaneously improve nitrogen-use efficiency and grain yield over what is currently achievable.