Guy Hanke

“I know of nothing sublime that is not some modification of power”   Edmund Burke

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Research Philosophy

The aim of my research is to identify the molecular and genetic mechanisms that control energy distribution in crop plants and cyanobacteria. We depend upon agricultural plants to supply our food and fossil plants to support most of our energy needs. This is possible because their autotrophic activity provides the energy to assimilate inorganic molecules and synthesize an incredible variety of useful products. A fundamental part of improving traditional agricultural crops and generating new microbial bioenergy crops will be to optimize energy distribution into metabolically engineered pathways.


So, how is energy generated photosynthetically? The flow of electrons through membrane complexes in the thylakoids of chloroplasts and cyanobacteria generates a supply of electrons at negative potentials (high energy) and a proton gradient (potential energy), which can be harvested to drive ATP synthesis, as shown in Figure 1. The reducing power of these electrons is harnessed primarily in fixation of C, but also in biosynthesis of a great many other important compounds. A "cyclic flow" is also possible, where electrons are returned to the membrane to boost the proton gradient, and thus ATP synthesis, in order to respond to changing metabolic demands. Transfer of these elcectrons to different processes is mediated by a group of proteins that are the main focus of work in the group: ferredoxins (Fd) and ferredoxin:NADP(H) reductases (FNR). We have found that an amazing diversity of these proteins, combined with dynamic changes in their location within the chloroplast, control the flux of electrons into different biosynthetic pathways and even back into cyclic electron transport. Electron transfer is inherrently dangerous - it generates free radicals that can cause damage, but also act as signals controlling plant stress responses and development. By studying these proteins we are finding out new things about stress tolerance and plant development.

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Figure 1. Photosynthetic electron transport. Light excitation of photosystem II (PSII) and photosystem I (PSI) results in electron transport through protein complexes in the thylakoid membrane. This drives proton pumping, resulting in a gradient that can be harvested for the synthesis of ATP. Ferredoxin (Fd) and Fd:NADP(H) oxidoreductase are at the pivotal point in either distributing electrons to metabolic pahways or returning them to the chain in a cyclic electron flow.