Professor David Day Present position: Dean of the Faculty of Science, The University of Sydney. Chief Investigator ARC Centre of Excellence in Plant Energy Biology Contact Details: Phone: 02-931514123 Fax: 02-93514124 Email: david.day@bio.usyd.edu.au
Selected Publications

CURRENT AND FUTURE RESEARCH DIRECTIONS

My current research attempts to marry traditional biochemistry/physiology approaches with those of molecular biology and genomics to solve problems in the regulation of cellular processes in plants. We focus on the biochemistry, molecular biology and genomics of electron and ion transport processes, and associated pathways of carbon and nitrogen metabolism in plants. While this is essentially fundamental research on plant mitochondria and symbiotic membranes, practical applications may arise from the results obtained as new concepts and observations are used to direct the production of new crop plants. For example, manipulation of fundamental aspects of electron transport in mitochondria can generate plants with altered respiration and possible commercially important traits. Our studies on transport mechanisms in symbiotic membranes of legumes are finding new processes, which have relevance to nutrient acquisition in general in plants.

Symbiotic nitrogen fixation

		Within a legume root nodule, nitrogen-fixing bacteroids are enclosed in a plant membrane, the symbiosome membrane (s), which effectively excludes the microsymbiont from the host cell's cytoplasm and controls all exchanges between the symbiotic partners. This structure is common to the majority of endosymbiotic associations found throughout nature, including some parasitic associations such as Legionnaires disease. Results we obtain with legumes such as soybean may, therefore, be pertinent to a wide range of different systems. My research group pioneered a study of this membrane and its transport properties.
We have identified a number of transport proteins on the symbiosome membrane of soybean and are now isolating the genes encoding these proteins. Details of their structure and the regulation of their expression may allow us to modify their activity and improve the efficiency of this agriculturally important process. To date we have isolated cDNA clones encoding proteins involved in ammonium transport, iron and zinc transport, malate transport and membrane energisation (H+-ATPases). Future work will focus on characterising these transporters and discovering new transport proteins, utilising the Medicago truncatula genomic database.

Mitochondrial metabolism and oxidative stress

Mitochondria are the sub-cellular organelles responsible for oxidative phosphorylation and consequently are essential for the growth and survival of all eukaryote organisms. In addition to their primary role in the energy balance of cells, plant mitochondria play important roles in floral development and fertility, they underlie the respiratory bursts which drive the climacteric of certain fruit and thermogenesis in some plants, and they are the site of several biosynthetic pathways (eg, folic acid, lipoic acid and vitamin C). Mitochondria have been implicated in systemic acquired resistance against viruses and they are also involved in programmed cell death (apoptosis). The latter phenomenon is likely to be particularly important in the hypersensitive response to pathogen attack in resistant plants and during senescence of plant organs. Mitochondria are also a site for generation of Reactive Oxygen Species (ROS). ROS generation occurs in response to many environmental stresses and it is essential that mitochondrial involvement in these responses be understood. Finding the genes and proteins that initiate and control the functions and interactions of mitochondria in plants (ie, the functional genomics of mitochondria), utilising the Arabidopsis and rice genome data bases, is the foundation of our current work in this area.