Interactions across the symbiosome membrane in soybean nodules

30 March 2012

Dr Penny Smith hosted by Robyn Overall

Nitrogen is crucial for plant growth and nitrogen fertilizers still make large contributions to agricultural production. However substituting biological nitrogen fixation (BNF) for fertilizer N is a key part of improving the sustainability of agricultural production owing to the energy intensity of fertilizer production and issues associated with excessive fertilizer use. BNF relies on symbioses between legumes and rhizobia, and allows plants to growwithout N fertilisers. Arguably BNF is perhaps the most economically important of all symbioses.

The symbiosome is the central part of this interaction; it is an organelle surrounded by the plant-derived symbiosome membrane (SM) in which rhizobia fix atmospheric N. Once engulfed in the SM the rhizobia rely on the plant for all their nutrients and this nutrient exchange across the SM effectively controls thesymbiosis.

We have been characterising the symbiosome membrane and the transport proteins that are present on the membrane. In exchange for nitrogen fixed by the bacteroid, the plant provides reduced carbon, probably in the form of malate, to the bacteroids, as well as other solutes including iron, sulphate and zinc. Although characterised biochemically, the molecular nature of most of the transporters is not known. We have used a proteomic approach to identify components of the soybean SM and are now characterizing the proteins and the genes encoding them by utilising information from both the genome and the transcriptome. We have a particular interest in potential transporters for malate from the POT/PTR family and metal transporters. We are using GFP-fusions to confirm their localisation to the SM, gene silencing to investigate their importance to the symbiosome and heterologous expression in yeast to functionally characterise the transporters.

Time: 4-5pm

Location: DT Anderson Lecture Theatre, A08