How plants fine-tune their natural chemical defenses

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Washington, September 8 : A new research has found out how plants fine-tune their natural chemical defenses.

Even closely related plants produce their own natural chemical cocktails, each set uniquely adapted to the individual plant's specific habitat.

Comparing anti-fungals produced by tobacco and henbane, researchers at the Salk Institute for Biological Studies in California, US, discovered that only a few mutations in a key enzyme are enough to shift the whole output to an entirely new product mixture.

Making fewer changes led to a mixture of henbane and tobacco-specific molecules and even so-called "chemical hybrids," explaining how plants can tinker with their natural chemical factories and adjust their product line to a changing environment without shutting down intracellular chemical factories completely.

The findings not only gave the Salk scientists a glimpse of the plants' evolutionary past, but may help them fine-tune the production of natural and environmentally friendly fungicides and pesticides as well as new flavors and fragrances by turning "enzymatic knobs" in the right direction.

Trying to make the best of their real estate, plants rely on an impressive arsenal of volatile and nonvolatile molecules, which diffuse easily through the membranes of the cells that produce them to communicate and interact with the outside world.

"Most people are familiar with the word biodiversity, but 'chemodiversity,'-the extraordinary tapestry of natural chemicals found in plants-is just as important for life, the appearance of new species and the survival of many different ecosystems on the earth," said Howard Hughes Medical Institute investigator Joseph P. Noel, who led the study.

"Understanding the chemistry and evolutionary principles that underlie this extraordinary biological diversity will show us how to alter biosynthetic pathways to equip crops with natural and environmentally friendly defenses against pests and diseases, to produce new pharmaceuticals, to enhance levels of naturally occurring health-promoting nutrients or to speed up plant adaptation in the face of global climatic change," said Noel.

For the current study, postdoctoral researcher Paul O'Maille, probed the metabolic pathways that members of the nightshade family, which includes tobacco, tomatoes, potatoes, peppers and henbane, use to produce terpenes-compounds that impart aromatic odors and flavors to foods.

O'Maille created a gene library that encoded all possible amino acid combinations, 512 in total, and produced and analyzed the mutant proteins, paying specific attention to the chemical output and efficiency of each enzyme.

This first glimpse revealed a rugged landscape of catalytic activities, where small changes gradually shift the equilibrium between both phytoalexins and in some cases cause rapid evolutionary jumps.

"It isn't the specific amino acid change that's important but rather the genetic context in which it occurs," said O'Maille.

Now, the Salk researchers are planning to extend their studies to other members of the nightshade family, including tomato, potato, pepper and eggplant, to see how Mother Nature recapitulates the simplified laboratory system.

ANI

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