Heterotrimeric G-protein interactions are conserved despite regulatory element loss in some plants

Heterotrimeric G-proteins are key modulators of multiple signaling and development pathways in plants and regulate many agronomic traits, including architecture and grain yield. Regulator of G-protein signaling (RGS) proteins are an integral part of the G-protein networks; however, these are lost in many monocots. To assess if the loss of RGS in specific plants has resulted in altered G-protein networks and the extent to which RGS function is conserved across contrasting monocots, we explored G-protein-dependent developmental pathways in Brachypodium distachyon and Setaria viridis, representing species without or with a native RGS, respectively. Artificial microRNA-based suppression of Ga in both species resulted in similar phenotypes. Moreover, overexpression of Setaria italica RGS in B. distachyon resulted in phenotypes similar to the suppression of BdGa. This effect of RGS overexpression depended on its ability to deactivate Ga, as overexpression of a biochemically inactive variant protein resulted in plants indistinguishable from the wild type. Comparative transcriptome analysis of B. distachyon plants with suppressed levels of Ga or overexpression of RGS showed significant overlap of differentially regulated genes, corroborating the phenotypic data. These results suggest that despite the loss of RGS in many monocots, the G-protein functional networks are maintained, and Ga proteins have retained their ability to be deactivated by RGS.