Molecular Plant Physiology – Dr Spencer Whitney

The research within my laboratory focuses on the photosynthetic enzyme Rubisco. This enzyme is essential for carbon acquisition by the biosphere. The properties of Rubisco, and their effect on photosynthesis, dictate the efficiency with which plants use their resources of water, nutrients and light. However, Rubisco is inefficient; its catalytic process is slow and it has difficulty distinguishing CO2 from the much more abundant gas, O2.
The driving theme of my groups' research is to understand the reasons for Rubisco's inefficiency and examine ways in which to engineer and transplant more efficient versions into crop plants to improve their resource use efficiency

Honours and PhD projects are available within the following research themes:

What makes Rubisco tick?
Research projects are available that are aimed at improving our fundamental understanding of the function and necessity of Rubisco N-terminal modifications and 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 using plastid chloroplast transformation technology. A number of mutant transgenic lines producing a foreign or mutated Rubisco are already available for molecular, biochemical and physiological analysis.

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 a high carboxylation efficiency. 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 via the surgical precision of plastome transformation.

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.

Techniques used
Molecular biology: Biolistic chloroplast genome (Plastome) transformation; PCR, DNA mutagenesis, DNA and RNA blot analyses.

Protein biochemistry: protein purification from plants, algae and bacteria; protein stability analysis, enzyme kinetics; mass spectrometry.

Photosynthetic physiology: leaf gas-exchange, stable-isotope mass spectrometry, metabolite analysis.

Useful papers
(Review) Mueller-Cajar O 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.

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.

(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.

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