Research Group Biochemical Ecology and Molecular Evolution

Evolution of enzymes involved in secondary metabolism of plants (Group E. Kaltenegger)

Evolution and biodiversity are two closely entangled fields of biology. Simply spoken - understanding evolutionary processes that led to today’s biodiversity can guide future perspectives to maintain the diversity in the ecosystems surrounding our daily life. Adaptation - like the development of resistance of pathogens (plant or human) – as one central driver of biodiversity, can only be properly understood in the light of evolution. And given the cellular basis of life, studying evolution should ultimately begin with the evolutionary dynamics of proteins. And this is exactly what this group is aiming for.

We use the tropic Morning Glories (Convolvulaceae), which are known for their beautiful flowers, as model organisms. Various species of this plant family produce specific plant secondary metabolites, namely the pyrrolizidine and tropane alkaloids (PAs and TAs). Both classes of alkaloids function in the plants defence against herbivores. While TAs are found in a broad range of species, PAs only occur in individual species. Thus, we postulate that TA biosynthesis is older compared to PA biosynthesis. Of note, both biosynthetic pathway show some striking similarities.

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The metabolic enzymes, which are involved in alkaloid biosynthesis, are excellent models to study evolutionary dynamics of proteins. As part of secondary metabolism, they are subject to rapid changes, because plants should deal with an army of herbivores, which themselves adapt to the plants defense – a classic ecologic phenomenon described as the “plant-herbivore arms race”. Based on this phenomenon, only plants that evolve through mutations new traits to warn of herbivores will survive.

One special type of mutations is central to our research: gene duplication. Many of the above-mentioned enzymes, that are involved in alkaloid biosynthesis, originated from a duplication. We are particularly interested in the following questions: how can duplicated genes gain new functions? Which molecular mechanisms are shaping a duplicated gene? Presently, by studying the evolution of the PA-biosynthesis specific homospermidine synthase (HSS) and the TA-biosynthesis specific putrescin-N-methyltransferase (PMT) within the Morning glories, we are trying to answer this question. Of note, both genes originated by duplication and gained a new function. Step by step we are now reconstructing HSS and PMT evolution in the ancestors of the today living Morning Glory species. With this approach, we aim to identify the mutations, which were involved in the change of function.

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