Research in the Marinus Pilon lab
Acquiring metals for photosynthesis: biogenesis and evolution of the electron transport chain. An issue of love and hate and why nothing else matters!

My group investigates iron and copper delivery to the photosynthetic machinery in plants. We use a combination of plant physiology, cell biology, biochemistry and molecular biology and genetics approaches in Arabidopsis thaliana to unravel the mechanisms involved and their regulation. Metals are indispensable for life as we know it; which is highlighted by the electron transport functions of redox-active metals (Fe, Cu and Mn) in respiration and photosynthesis. Living organisms devote a significant part of their genome to metal homeostasis: having enough essential metals while avoiding toxic levels. Metal ion homeostasis touches daily life (zinc-oxides in sun screens promote zinc resistant algal growth in lakes, Cu as a component of anti wrinkle cream replenishes the Cu required for cross-linking of skin proteins), agriculture (iron availability limits productivity particularly in alkaline soils) and medicine (several of the most common genetic diseases are caused by metal ion imbalances, pathogenic microbes compete with the host for metal ions, such as iron, the outcome of the fight over these metals may be a matter of life and death).

My group studies Fe and Cu cofactor delivery and assembly in plastids, the organelle responsible for photosynthesis in plants. Metal ion biology in plants is particularly interesting because it is vital to plant productivity and nutritional value (an estimated 50% of the world's population living mainly of vegetarian diets may be deficient in iron due to the low amounts of Fe in edible parts of plants). My interest in the field is further fueled by the obvious need within an organism for regulation and communication involved in metal ion use; furthermore, the relation to the build up and evolution of a complex machinery present in the chloroplast is fascinating.

Our research can be placed in the context of the history of metal ion use by living organisms. Iron is highly suitable for the various redox and catalytic functions that were required for early life and iron is very abundant in the earth's outer crust. It is hypothesized that after an early addiction of life to iron, oxygen poisoning of the atmosphere by cyanobacteria has led to new constraints on metal ion use. This is, because oxygen promotes the formation of ferric oxides, which are insoluble, thus oxygen depleted the world of usable iron, which nowadays is very hard to obtain. Therefore, present day organisms must compete for iron. A nasty side effect of the oxygen rich atmosphere is the tendency of oxygen to destroy Fe based cofactors (iron sulfur clusters and haem). Perhaps not of significance earlier, the more scarce Cu became important as a cofactor to help cells deal with redox chemistry involving oxygen, but life is still hooked on iron and Fe remains as the most important metal ion. In addition to depleting iron, oxygen can be converted to damaging radicals and other reactive oxygen species, a process which is promoted by free redox-active metal ions such as Fe and Cu. Interestingly, the enzymes that have evolved to deal with the reactive oxygen species again use metal cofactors. Thus life has developed a love-hate relationship with metal ions.

Clearly the problem that all organisms must deal with is how to get sufficient metal ions while avoiding toxicity. The problem is not trivial in a unicellular organism but in even more highly compartmentalized Eukaryotes such as the plant Arabidopsis thaliana the problem is formidable. After all some metals much reach compartments such as the chloroplast where photosynthesis takes place and have to pass through areas where their presence is less desired. How is that achieved? Organisms use a combination of metal transporters, soluble metal binding proteins and regulators to achieve metal homeostasis. Our lab tries to figure out which components work in getting metals to the photosynthetic machinery, and how the complex dance of the metals is orchestrated. The importance of metal ion delivery to plastids is illustrated by the phenotype of plants that are defective in metal ion delivery, these plants are deficient in photosynthesis and thus primary mass production, a process we all depend on for our food.

Research into metal biology in plants has been a real adventure so far: see our publications for more details. I am sure we are still in the beginning phase of our discoveries. In the end, I am convinced that whatever we will find, the field of heavy metal biology really rock and a famous heavy metal band may have been right all the way: nothing else matters.