Molecular and physiological studies of nitrogen uptake in plants and fungi

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During the last fifty years, global nitrogen fertilizer use has climbed to approximately 100 billion kg per annum at a cost of about 50 billion dollars. Much of this fertilizer is leached from the land and swept into rivers and oceans, where it causes considerable environmental damage to natural populations through blooms of microrganisms. Their rapid growth reduces oxygen levels in coastal waters e.g. in the Gulf of Mexico, where this periodically results in large fish kills. The increasing population growth and degradation of agricultural lands worldwide can only exacerbate this problem in the coming years.My research focusses on the physiological and molecular mechanisms that regulate nitrogen uptake by plant roots. Membrane transport of nutrients is a fundamental part of the biology of plants; it is also of considerable practical importance from an environmental and economic standpoint. Root nitrate uptake is mediated by a 50 kDa membrane protein common to organisms from fungi to higher plants. We have shown this protein (nrt2.1) requires the participation of a second smaller protein (nrt3.1). We have successfully expressed the two proteins in a fungus (Aspergillus nidulans) in order to study the basis of the protein interactions using site-directed mutagenesis. We will use fluorescence microscopy to explore interactions between fluorecently tagged recombinant nrt2.1 and nrt3.1 proteins and immunoprecipitation to verify the proposed dimeric functional unit. Related to this project we have shown that the fungal nitrate transporter is regulated posttranslationally, probably by an allosteric mechanism involving protein phosphorylation. Using site-directed mutagenesis of the fungal protein we seek to further explore this regulation. We are also investigating the functions of the five root amt1 ammonium transporters in Arabidopsis. We have experienced some preliminary success in increasing dry matter yield in tobacco by overexpressing nrt2.1 and nrt3.1. It is feasible that the knowledge we gain may enable us to make further improvements. My research involves collaborations with scientists in Canada, Australia, Scotland, Iran and India and we regularly receive visiting scientists and graduate students at UBC.