Dr Spencer Whitney

Molecular Plant Physiology
Research School of Biological Sciences
GPO Box 475
Canberra ACT 2601
ph: +61 (02) 6125 5073
fax: +61 (02) 6125 5075

email: Spencer.Whitney@anu.edu.au

Information for prospective students

Current position

Research Fellow

Research interests

My research focuses on the genetic manipulation of Rubisco, the central CO2-fixing enzyme of photosynthesis. This research provides training in molecular biology, protein engineering (directed evolution), enzyme kinetics, biochemistry, plastome transformation, tissue culture and whole plant physiology.

Photosynthesis and plant growth

Improving the ability of crops to use water, light and fertiliser more efficiently would have economic benefits and ease the environmental impacts associated with agricultural practices. It is thought that such improvements can be made by enhancing the efficiency of the photosynthetic CO2 -fixing enzyme Rubisco which is responsible for the fixation of almost all of the CO2 in the biosphere. We are utilising Chloroplast transformation as a key technology to transplant altered or foreign Rubiscos into our model plant tobacco and assess the biochemical and physiological consequences of the engineered changes. This work has allowed us to test the mathematical models of photosynthesis and gain valuable insight into post-translational processing and assembly of proteins in the chloroplast. This work comes under the following two research programs-

1. Adapting from nature

Rubisco in higher plants is not the pinnacle of evolution. We have identified more efficient Rubiscos in non-green algae that can discriminate twice as effectively against O2 while maintaining higher carboxylation efficiencies. Even within higher plant species there is significant diversity in their kinetics. Projects are available to characterize the genetic and biochemical properties of diverse Rubiscos and use this information to engineer, or directly transplant, better versions into plant plastids.

2. What makes Rubisco tick?

A variety of research projects are focused on improving our fundamental understanding of

(1) the function and necessity of the co- and post-translational modifications that are made to the catalytic Rubisco large subunit and

(2) explore which residues in Rubisco and its helper protein, Rubisco activase, influence their selective interaction.

This information is paramount for our ongoing efforts to engineer and transplant more efficient Rubisco into crops. A number of mutant transgenic lines producing a foreign or mutated Rubisco are already available for molecular, biochemical and physiological analysis.

Laboratory evolution of Rubisco

Directed evolution is a powerful protein engineering tool that entails the generation of large libraries of random mutants of a gene that are screened by a selection system to identify gene products with a more desirable (“improved”) function. We have developed a novel Escherichia coli strain that is dependent on Rubisco expression for growth. Projects are available to use this E. coli strain to screen mutated libraries of different Rubisco genes to screen for variants with unique biophysical and kinetic properties.

Selected Publications

Directed evolution of Rubisco

(review) Mueller-Cajar and Whitney S.M. (2008) Directing the evolution of Rubisco and Rubisco activase - first impressions of a new tool for photosynthesis research. Photosynthesis Research, in press

Mueller-Cajar and Whitney S.M. (2008) Evolving improved Synechococcus Rubisco functional production in Escherichia coli. Biochemical Journal,414, 201-214

Mueller-Cajar O, Morell M, Whitney S.M. (2007) Directed evolution of Rubisco in E. coli reveals a specificity-determining hydrogen bond in the Form II enzyme. Biochemistry, 46, 14067-74

Greene D.N, Whitney S.M, Matsumura I. (2007) Artificially evolved Synechococcus PCC6301 Rubisco variants exhibit improvements in folding and catalytic efficiency. Biochemical Journal, 404, 517-24

Plastome engineering of Rubisco

Whitney S.M and Sharwood R.E (2008) Construction of a tobacco master line to improve Rubisco engineering in chloroplasts. Journal of Experimental Botany, 59, 1909-1921

Sharwood R.E, von Caemmerer S, Maliga P and Whitney S.M. (2008) The catalytic properties of hybrid Rubisco comprising tobacco small and sunflower large subunits mirror the kinetically equivalent source Rubiscos and can support tobacco growth. Plant Physiology, 146, 83-96

Whitney, S.M and Sharwood R.E (2007). Linked Rubisco subunits can assemble into functional oligomers without impeding catalytic performance. Journal of Biological Chemistry, 282, 3809-3818

Whitney, S.M. and Andrews, T.J. (2003) Photosynthesis and growth of tobacco with a substituted bacterial Rubisco mirror the properties of the introduced enzyme Plant Physiology, 133, 287-294

(Review) Andrews, T.J. and Whitney, S.M. (2003) Manipulating rubisco in the chloroplasts of higher plants. Archives of Biochemistry and Biophysics 414: 159-169.

Whitney, S.M. and Andrews, T.J (2001) Plastome-encoded bacterial ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) supports photosynthesis and growth in tobacco. Proceeding of the National Academy of Sciences 98: 14738-14743.

Whitney, S. M. and T. J. Andrews (2001) The gene for the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit relocated to the plastid genome of tobacco directs the synthesis of small subunits that assemble into Rubisco. Plant Cell 13: 193-205.

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