Profiling plants to identify new high-value substances

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MSU research assistant Nate Durussel with stevia plants  (view larger image)

In the emerging field of metabolomics — the science of studying small molecules (metabolites) — Michigan State University (MSU) is a pioneer. The mass spectrometer, an analytical instrument housed in the laboratory of MSU AgBioResearchscientist A. Daniel Jones, is busy working 24 hours a day measuring unique chemical imprints left behind by plant cells.

Research assistant Nate Durussel with Stevia plants he is propagating in an MSU greenhouse.
Photos courtesy of A. Daniel Jones

Plants are the most chemically prolific organisms on the planet, producing a wide range of chemical compounds. Society places high value on many of these substances for medicinal purposes, insect or disease resistance, flavors and aromas (perfumes). Plants utilize these chemicals to attract pollinating insects or repel damaging pests and predators.

Though scientists have developed efficient ways to breed plants to produce high yields, they haven’t been as successful at figuring out how to cultivate the high-value chemical products of plants. Little is known about the majority of plant chemicals, the purposes they serve or how they are produced. One example is stevia, a group of natural sweeteners produced by the Stevia plant. (Steviais much sweeter tasting than sugar, so smaller amounts can be used to achieve the same levels of sweetness.)

A procedure using the mass spectrometer to perform molecular profiling of thousands of Stevia plants was developed by AgBioResearch horticulturists Randy Beaudry and Ryan Warner in collaboration with Jones. This technique will help to identify individual plants that consistently and reliably produce sweet-tasting compounds and guide plant breeding efforts to improve the quality and yields of steviasweeteners.

In two other projects, Jones has teamed up with several AgBioResearch colleagues. One project with C. Robin Buell andMary Hausbeck is using genomic and metabolomic analyses to improve breeding of American ginseng.  In another project, Jones is working with Robert Last and Cornelius Barry and University of Michigan professor Eran Pichersky on the specialized cells on the surface of the tomato plant that produce the scent that lingers after you brush up against it. The chemicals responsible for this aroma make up an arsenal of chemical defenses, many of which accumulate in trichomes (tiny hairlike glands) lining the leaves and stems. Knowledge of the genes responsible for these chemicals may provide clues to what regulates the production of chemicals in other plants.

“By understanding how trichomes produce these chemical compounds, we may be able to breed or engineer plants that make more of a specific substance,” said Jones, a professor in the MSU Department of Biochemistry and Molecular Biology. “We could reintroduce some of the genes from wild relatives of tomato into conventional tomato varieties to make them more insect-resistant.”

Genes that researchers discover may eventually be used to launch another biotech revolution — generating new industries that make valued components from plants.

“Figuring out how plants produce these high-value substances in large quantities could help make the agricultural and biotechnology industries in Michigan and across North America more competitive,” Jones said.

Jones and other researchers, led by MSU AgBioResearch scientist Dean DellaPenna, have just completed an online medicinal plants metabolomic resource for multiple tissues of 14 medicinal plant species. The information is hosted on the National Institute of Health’s website, which was developed by Professor Eve Wurtele and her team at Iowa State University.  This resource, coupled with its associated medicinal plants genomics resource, will enable individuals to link the amounts of medicinal chemicals in specific plant tissues with genes expressed in those tissues.  Armed with this information, researchers, including plant breeders, can exploit these genes to improve production of medicines in plants or microbes.

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