Down-regulated Lotus japonicus GCR1 plants exhibit nodulation signalling pathways alteration

G Protein Coupled Receptor (GPCRs) are integral membrane proteins involved in various signalling path-ways by perceiving many extracellular signals and transducing them to heterotrimeric G proteins, whichfurther transduce these signals to intracellular downstream effectors. GCR1 is the only reliable plant can-didate as a member of the GPCRs superfamily. In the legume/rhizobia symbiotic interaction, G proteinsare involved in signalling pathways controlling different steps of the nodulation program. In order toinvestigate the putative hierarchic role played by GCR1 in these symbiotic pathways we identified andcharacterized the Lotus japonicus gene encoding the seven transmembrane GCR1 protein. The detailedmolecular and topological analyses of LjGCR1 expression patterns that are presented suggest a possibleinvolvement in the early steps of nodule organogenesis. Furthermore, phenotypic analyses of indepen-dent transgenic RNAi lines, showing a significant LjGCR1 expression down regulation, suggest an epistaticaction in the control of molecular markers of nodulation pathways, although no macroscopic symbioticphenotypes could be revealed.