Scientists at the Salk Institute for Biological Studies and Iowa State
University discovered a
family of plant proteins that play a role in the production of seed oils,
substances important for animal and human nutrition, biorenewable chemicals,
and biofuels.
Scoring a rare scientific hat trick, the researchers identified three
related proteins in thale cress plants (Arabidopsis thaliana) that
regulate the metabolism of fatty acids, chemical components of all cell
membranes and vegetable oils. They dubbed these fatty-acid binding proteins
FAP1, FAP2, and FAP3.
The findings, reported in Nature, may lead to the development of
improved crops yielding higher qualities and quantities of oils, helping to
address growing demands for food and fuel and the consequent environmental
pressures on the world’s ecosystems.
“This work has major implications for modulating the fatty acid
profiles of plants, which is terribly important, not only to sustainable food
production and nutrition but now to biorenewable chemicals and fuels,”
says Joseph Noel, director of Salk’s Jack H. Skirball Center for Chemical
Biology and Proteomics and a Howard Hughes Medical Institute (HHMI)
investigator, who led the multidisciplinary study together with Eve Syrkin
Wurtele, professor of Genetics, Development and Cell Biology at the Plant
Research Institute at Iowa State.
“Because very high-energy molecules such as fatty acids are created in
the plant by solar energy,” says Wurtele, “these types of molecules
may ultimately provide the most efficient sources for biorenewable
products.”
Plant oils are composed primarily of triglycerides, formed by linking
together three fatty acid molecules, and are stored mostly in seeds, where they
are used for energy during germination. Seeds are crucial sources of oils for
nutrition, flavoring and industrial applications, such as the manufacture of
soap and cosmetics and for biofuels. With growing concerns about global climate
change and petroleum security, producing biofuels for use in transportation and
energy generation is a burgeoning industry.
To help address this demand, scientists are unlocking the molecular pathways
involved in seed oil metabolism in hopes of finding ways to boost capacity and
quality.
In their study, Noel and his collaborators identified three promising genes
through analysis of plant genomic data, and then used a variety of techniques,
including protein X-ray crystallography, computational biology, biochemistry,
mutant plant analysis, metabolomics, and gene expression profiling, to
functionally characterize the proteins these genes produce.
They found that the proteins, FAP1, FAP2, and FAP3, bind fatty acids,
including the major plant omega-3 fatty acid, an important nutritional
component found in certain seeds. “They say a picture is worth a thousand
words, and that is certainly the case for these FAPs,” says Gordon Louie,
an HHMI researcher in Noel’s laboratory, who determined the three-dimensional
arrangement of the FAPs holding on to their fatty acid cargo.
The proteins were found in the chloroplasts, the site of fatty acid
production and photosynthesis. This suggested that these proteins play a role
in the metabolism of fatty acids and thus in the production of fatty acids for
plant membranes and oils.
This hypothesis was reinforced by showing that the FAP genes are most active
in developing seeds, appearing at the same time and location as well-known
enzymes involved in fatty acid synthesis. The researchers also found that
altering the expression of these genes in a plant leads to changes in the quality
and amounts of fatty acids.
“The proteins appear to be crucial missing links in the metabolism of
fatty acids in Arabidopsis, and likely serve a similar function in other plant
species since we find the same genes spread throughout the plant kingdom,”
says Ryan Philippe, a postdoctoral researcher in Noel’s laboratory.
Micheline Ngaki, a graduate student in Wurtele’s laboratory, says that if
the researchers can understand precisely what role the proteins play in seed
oil production, they might be able to modify the proteins’ activity in new
plant strains to produce more oil or higher quality oil than current crops.
The researchers’ findings also have implications for evolutionary biology
and how large and essential families of enzymes arise from nonenzymatic cousins
and are then perfected by evolution.
The ancient ancestors of the proteins the research teams discovered evolved
into the enzyme chalcone isomerase, which plays a key role in the production of
a group of polyphenols known as flavonoids, compounds that serve a number of
functions in plants and are critical for disease prevention in human diets.
“One function of flavonoids is to protect plants from sunlight, which
would have been key when plants first emerged from the oceans and lakes to
colonize land,” says Noel. “We’ve shown that the very ancient FAP
proteins still found in algae and other non-plant organisms acquired chalcone
isomerase activity hundreds of millions of years ago, allowing land plants to
produce flavonoids for survival in the absence of the protective environment of
water.”
The discovery may also help bioengineers focused on creating new enzymes for
industrial uses by revealing how nature evolves proteins into chemical machines
known as enzymes.
“Nature has been perfecting enzymes for at least three billion years
because they carry out the hundreds of thousands of chemical reactions in all
organisms, and these reactions are needed by us all to survive and prosper,”
says Noel. “We could learn a lot by understanding that three-billion year
old experiment.”
