Background: Heterotrimeric G-proteins are important signalling switches, present in all eukaryotic kingdoms. In plants they regulate several developmental functions and play an important role in plant-microbe interactions. The current knowledge on plant G-proteins is mostly based on model angiosperms and little is known about the G-protein repertoire and function in other lineages. In this study we investigate the heterotrimeric G-protein subunit repertoire in Pinaceae, including phylogenetic relationships, radiation and sequence diversity levels in relation to other plant linages. We also investigate functional diversification of the G-protein complex in Picea abies by analysing transcriptional regulation of the G-protein subunits in different tissues and in response to pathogen infection.
Results: A full repertoire of G-protein subunits in several conifer species were identified in silico. The full-length P. abies coding regions of one Gα-, one Gβ- and four Gγ-subunits were cloned and sequenced. The phylogenetic analysis of the Gγ-subunits showed that PaGG1 clustered with A-type-like subunits, PaGG3 and PaGG4 clustered with C-type-like subunits, while PaGG2 and its orthologs represented a novel conifer-specific putative Gγ-subunit type. Gene expression analyses by quantitative PCR of P. abies G-protein subunits showed specific up-regulation of the Gα-subunit gene PaGPA1 and the Gγ-subunit gene PaGG1 in response to Heterobasidion annosum sensu lato infection.
Conclusions: Conifers possess a full repertoire of G-protein subunits. The differential regulation of PaGPA1 and PaGG1 indicates that the heterotrimeric G-protein complex represents a critical linchpin in Heterobasidion annosum s.l. perception and downstream signaling in P. abies.