Fig. 7: A proposed working model for GC1 regulates SbpPLAII-1 degradation and controls glume coverage.

G protein β subunit and G protein γ subunit GC1 could form a dimer to conduct a Gβγ-mediated signaling. SbpPLAII-1 functions as a positive regulator in glume cell proliferation by promoting the transcripts of Cyclin-CDK related genes. The G protein γ subunit can interact and promote the degradation of SbpPLAII-1. In wild type, the long tail of GC1 could increase the 26S proteasome-dependent degradation, resulting in an unstable protein level. This subsequently leads to a normal phospholipase SbpPLAII-1 level and results in a final high glume coverage phenotype in sorghum. However, the truncated gc1-a protein (short tail) is more stable than GC1 (long tail) due to the absence of C-terminus, and then enhances the degradation of SbpPLAII-1. It leads to a significantly inhibited SbpPLAII-1 signal involved in glume cell proliferation and therefore causes low glume coverage in sorghum.