Abstract
G-alpha (Gα) and ‘Regulator of G-protein Signaling (RGS)’ proteins are the two key components primarily involved in regulation of heterotrimeric G-proteins signaling across phyla. Unlike Arabidopsis thaliana, our knowledge about G-protein regulation in polyploid Brassica species is sparse. In this study, we identified one Gα and two RGS genes each from three species of Brassica ‘U’ triangle and assessed the effects of whole genome triplication on the divergence of gene sequence and structure, protein-protein interaction, biochemical activities, and gene expression. Sequence and phylogenetic analysis revealed that the deduced Gα and RGS proteins are evolutionarily conserved across Brassica species. The duplicated RGS proteins of each Brassica species interacted with their cognate Gα but displayed varying levels of interaction strength. The Gα and the duplicated RGS proteins of Brassica species exhibited highly conserved G-protein activities when tested under in-vitro conditions. Expression analysis of the B. rapa RGS genes revealed a high degree of transcriptional differentiation across the tested tissue types and in response to various elicitors, particularly under D-glucose, salt and phytohormone treatments. Taken together, our results suggest that the RGS-mediated regulation of G-protein signaling in Brassica species is predominantly governed by stage and condition-specific expression differentiation of the duplicated RGS genes.
Highlights
The core components of G-protein signaling are highly conserved across phyla, the plant and animal systems are known to have enormous diversity in their quantitative repertoire and regulation of G-protein cycle
RGS1 and BolC.RGS2 (B. oleracea), based on the standardized nomenclature adopted for Brassica genus[44]
Sequence analysis of the deduced RGS proteins of Brassica lineage on TMHMM server revealed the presence of an N-terminal ‘seven trans-membrane domain (7-TM)’ and a C-terminal located ‘cytosolic RGS-domain’ (Fig. 1A), similar to that reported for the Arabidopsis and soybean RGS proteins[15,45]
Summary
The core components of G-protein signaling are highly conserved across phyla, the plant and animal systems are known to have enormous diversity in their quantitative repertoire and regulation of G-protein cycle. The interplay between RGS and Gα proteins is quite important in regulating overall G-protein mediated biological processes in plants. Structurally similar across plant lineage, both Gα and RGS proteins interestingly possess distinct and species-specific functions. Species-specific roles of Gα and RGS proteins in plant lineage could be attributed to their distinct transcriptional and biochemical properties, as well as the involvement of their upstream regulators and downstream effectors. Complex networks of G-protein signaling have been recently reported in few Brassica species[10,43], detailed studies on the expression, biochemical, interaction and functional variance of the Gα and RGS proteins, arising from polyploidy, are fundamentally important for a better understanding of the regulation of G-protein signaling from globally cultivated Brassica crops
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