Novel signalling pathways in symbiosis

Project leader:  Dr Helen Irving

Plant growth is often limited by soil nitrogen and this has resulted in the evolution of symbiotic interactions between plants and prokaryotes.  The primary source (~80%) of symbiotic nitrogen fixation in agriculture is the rhizobia-legume symbiosis.  Rhizobia are soil bacteria that interact symbiotically with legumes to form nitrogen-fixing nodules in nitrate-poor soils.  Rhizobia excrete Nodulation (Nod) factors that initiate nodule formation in the host plant; root hairs are particularly responsive to Nod factors.  Nod factors are lipo-chito-oligosaccharides and their discovery over a decade ago has been very useful in untangling and identifying how the host plant responds to rhizobia.  Critical to optimising this interaction is understanding the cellular signalling events that occur in this dynamic interaction at both a molecular and biological (in planta) level.  In collaboration with Prof Bill Broughton (Université de Genève, Switzerland) and other members of the Phaseomics consortium, we are investigating the early host responses of legume root hairs to Nod factors. 

Several recent advances using Nod factors and genetic approaches have revealed some of the key events in the signalling cascade elicited by Nod factors.  Deformation of the root hairs in characteristic patterns is one of the earliest physiological responses to Nod factors. Thus it has been found using mutants that “do not deform” that receptor-like kinase proteins are important in perceiving the Nod factor at the surface of the root hair.  These recent genetic advances make it a very exciting period to be pursuing how the signalling cascade operates within the root hair.  We have identified various G-proteins and phospholipase C as two key components of the root hair deformation response.  We plan to investigate how G-proteins and phospholipase C interact with other aspects of the cellular machinery (e.g. protein phosphorylation cascades) to initiate the host symbiotic responses.  We will use an innovative combination of different fields and skills – Molecular Biology, Biochemistry, Bio-informatics, Genetics, Plant Physiology and Cell Biology – to pursue these studies.  Several PhD topics are available for study in this project.