17 August 2011
Analysis of biosynthesis in plants reveals a "perplexing disparity"
by Kate Melville
A fascinating new study appearing in the Journal of the American Chemical Society reveals that during the evolution of certain natural plant chemicals, nature doesn't settle for the "low-hanging fruit" but instead favors rarer, harder to synthesize compounds.
The lead authors of the new study, Dr Paul �Máille at the John Innes Centre and Joseph P. Noel at the Salk Institute, say that the evolution of the characteristic swirl shapes of Nautilus shells inspired them. Other research has shown that recurrent Nautilus designs have formed to cope with changing sea levels. Why these forms occur, and not others, is an important evolutionary question, and to answer this, an analytical technique known as theoretical morphology was developed.
Theoretical morphology involves the mathematical simulation of forms such as the possible shape and dimensions of the nautilus shell. This allows a comparison of theoretical and actual distributions to study the evolutionary significance of biological forms, past and present. �Máille and Noel decided to apply the same theoretical morphology techniques to the study of terpenes, a group of natural products produced by plants.
Plants like pepper, tomato, and potato (members of the Solonanceae family) synthesize a signature set of terpenes for chemical defense against pathogens. Terpenes are essential for the ecological viability of the plant but also provide important compounds for human use. Examples of well-known bioactive terpenes include taxol, which is used to treat certain cancers, and the anti-malarial drug artemisinin. Terpenes are also used as fragrances and flavorings, and their utility has made them the subject of much pharmaceutical research.
"The big question is how plants have evolved to make these chemicals," said �Máille. "Is there a physical explanation, based on the chemical reaction, for why certain terpenes are favored? Are plants simply making the easy to synthesize low hanging fruit of the terpene chemical world?"
To investigate these questions, the researchers applied theoretical morphology techniques to compare theoretical and actual abundances of terpenes from solanaceaous plants. "We discovered a perplexing disparity between the predicted and natural abundance of terpenes. The common terpenes we see in nature are predicted to be quite rare, based on the chemistry. On the other hand, the terpene forms predicted to dominate are scarcely seen in nature," explained �Máille.
He believes that nature reaches for the higher-hanging fruit, skewing chemical reactions to favor rarer chemicals. This suggests an adaptive significance to the distribution of chemicals produced by plants.
The distribution and diversity of plant terpenes in nature has yet to be exhaustively characterized, however, this study provides new insights into the physical processes that underlie terpene biosynthesis in plants and may reveal routes to rare or undiscovered natural products with potent bioactivities.
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Source: John Innes Centre