RGB1-DEP1 and RGB1-GGC2 dimers positively regulate grain size, while occupation of RGB1 by the GS3 protein disrupts such function (Sun et al., 2018). Such competitive interactions and antagonistic activities of these proteins play important role in grain size regulation. DEP1 and GGC2, when coupled with RGB1, promote grain length by tail (C-terminal cysteine rich daomain)-mediated signaling. GS3, though having no function in promoting or inhibiting grain size, reduces grain size by blocking the interaction of DEP1 and GGC2 with RGB1 (Sun et al., 2018). The tail-mediated self-degradation of GS3 in the RGB1-GS3 complex provides a dynamic balance between blocking and the DEP1/GGC2?RGB1 interaction. DEP1 and GGC2 function to promote grain length, which is essential for yield increase and GS3 plays a role to keep balance for maintaining fitness in response to natural selection (Sun et al., 2018).