FEAST focus #18 (11/2005, p.10)
We will follow the itinerary of Dr Timothy George, from the UK to his Marie Curie Outgoing Fellowship at CSIRO Plant Industry and his work on the plant/soil interface.
The project
All started at University of Reading (www.rdg.ac.uk), with Timothy’s participation in Peter Gregory’s team in the Department of Soil Science. The team is well connected with the European “rhizosphere” community, including by participating in a European COST action, and with strong links with Philippe Hinsinger at INRA (Montpellier France).
Tim successfully responded to an international competitive Postdoctoral fellowship from the Plant Industry CSIRO Division to work with Alan Richardson at Black Mountain (Canberra). Encouraging results obtained by Tim convinced him to stay a bit longer.
In early 2004 he applied for different fellowships and grants including through the EC Marie Curie scheme, the Biotechnology and Biological Sciences Research Council (BBSRC, www.bbsrc.ac.uk)
and the Natural Environment Research Council (NERC,
www.nerc.ac.uk). Despite a long decision time, the Marie Curie fellowship was the first to come through. This scheme is more generous than many other equivalent fellowships.
Outcomes
Once the fellowship is granted the process is quite transparent. The financial support is directly managed by his institution in the UK, including managing all the paperwork with the host organisation in Australia (here the CSIRO). Tim reckons that the whole process is so smooth that he never met or heard from any one in the Marie Curie office in Brussels.
A large proportion of endogenous soil P is organic, of which derivatives of inositol phosphates (i.e. phytate) constitute a major fraction. The bioavailability of inositol phosphates depends on their mineralization by extracellular phytases.
At CSIRO Tim concentrates on expressing genes in plants for the production of phytases with biochemical traits that effect their interaction with soil. He worked on transgenic Trifolium subterraneum (clover) expressing a phytase gene (phyA) from Aspergillus niger (a fungus). These transformed lines showed an average increase in exuded phytase activity. Unlike other phosphatases, exuded phytase activity was unaffected by P supply, verifying the constitutive expression of phyA. Despite variable growth and P nutrition responses, P uptake per root length was on average greater for transgenic lines. Exudation of phytase by transgenic T. subterraneum allowed utilization of P from phytate in nonsorbing, sterile laboratory media, but was less effective when plants were grown in soil. Release of extracellular phytase is shown not to be the only requirement for the acquisition of P from endogenous soil phytate by plants. Moreover, inhibition upon adsorption of phytase has been shown to be soil specific, particularly in terms of soil texture and mineralology. Changes in rhizosphere pH may also affect the adsorption reactions of phytase in soils.
Future
Professor Peter Gregory was appointed in April 2005, as the new Director of the Scottish Crop Research Institute (SCRI, www.scri.sari.ac.uk) near Dundee in Scotland. Once returned to the UK, Tim will join SCRI for the one year reintegration phase of the fellowship. Both teams want to build on the opportunity that rose from an international PostDoc.
The “People” programme of the FP7 will maintain the Marie Curie Actions. They are a significant opportunity open to Australian researchers.
The Challenge
At present little is known about the efficacy of phosphatase-organic P (Phosphate) interactions in soils, other than that increases in soil phosphatase activity are associated with increased P uptake by certain plants. Generally, our understanding of the fate of phosphatase enzymes upon entering the rhizosphere is poor. Even less is known regarding the nature of the P compounds mineralised by the specific phosphatases in the rhizosphere. This project quantifies the fate of phosphatases in the rhizosphere and their interaction with organic P substrates in the soil environment. The contribution of phosphatase to P nutrition of plants is quantified and the potential for improving the P-use efficiency of crops will be determined.
The approaches used in fulfilling these objectives are highly novel. Very few studies of phosphatase in the soil environment have been done specifically in the rhizosphere because of the difficulties of working in this zone. However, this study uses novel tools such as transgenic plants to specifically alter the rhizosphere environment in-situ. Spatial, biological, chemical, physical and biochemical attributes of the rhizosphere are measured using “rhizobox” technology. Labelled antibodies specific to the phytase exuded by these plants are available and can be used in conjunction with fluorescent labelling and confocal microscopy, to trace spatial aspects of the phosphatase-substrate reaction in the rhizosphere and to assess the soil chemistry condition the enzyme is associated with. The integration of these novel techniques with standard techniques for soil chemical, biological and biochemical analysis, including chemical extractions, enzyme assays and isotopic labelling of soils allows a completely new approach to tackling the limitations to phosphatase efficacy in the rhizosphere and implement training in a unique combination of skills and techniques.
