Meet the genes in the beans of your coffee
Wake up
and smell the genome.
Researchers
have pieced together the genetic atlas of the parent of the most commonly
cultivated species of coffee plant and uncovered a rather independent streak in
its evolution.
Coffee
developed its caffeine-generating capacity independently from its cousin,
cacao, according to the first whole genome study of the plant behind the brew
quaffed every morning by about 100 million Americans, published online Thursday
in the journal Science.
There’s
been a lot of genetic sleuthing on coffee, most of it far from the tree. We
have a good idea about how caffeine affects animal (particularly human) genes
and alters brain chemistry. We know which of our own genes seem to draw us
toward consuming coffee, tea or chocolate as well. And there’s also been a
heady, if somewhat contradictory, brew of studies purporting to demonstrate
caffeine’s beneficial and deleterious effects on humans.
But how
caffeine production got started has been as hard to see as a spoon in a
demitasse of espresso.
“Coffee
has been kind of an orphan crop," said UC Davis geneticist Juan
F. Medrano, who was not involved in the study. "It has been kind of
forgotten in terms of DNA research. Perhaps this opens the door to expand that
area.”
The international team that spent years
piecing together coffee's massive genome suggests that a caffeine chemical
factory developed independently at least twice, in cacao and coffee, in what's
known as convergent evolution. (Koalas and humans, for instance, have
fingerprints, and widely divergent animals have developed prickly outsides to
protect their gooey insides.)
Compared with its close relatives, coffee
harbors larger families of the genes linked to aroma and bitterness and has a
wider array of genes linked to caffeine production, the study found.
How those new genes popped up and
proliferated appears to be a series of small, fortuitous accidents, the study
suggests. Neighboring genes were duplicated by a process roughly equivalent to
erratic coding and processing in a computer. Unlike computers, biological
systems are ruthless housekeepers, shucking duplicates like excess baggage.
Sometimes duplicates develop their own specialty, which appears to be what
happened in the case of coffee, the authors suggest.
“A small percentage of them survive, either
by splitting functions or evolving new ones," said study coauthor Victor
A. Albert, an evolutionary biologist at the University at Buffalo, part of the
State University of New York. "In the case of caffeine genes, we have a
series of duplications that occurred all next to each other, which gave rise to
enzymes that catalyze different steps" in caffeine production.
Evolution favored caffeine production because
the compound repels insects that prey on leaves and halts the germination of
seeds from competing plants, giving coffee species a niche in which to thrive.
Recent research also has suggested caffeine can help orient beneficial
pollinators toward the coffee flower, Albert said.
Duplication of an entire genome is thought to
be a primary driving force in the rise of new species and the wide
diversification of life. But coffee appears to have taken a slower, piecemeal
approach of small duplications. That could mean biologists have been underestimating
the contribution of narrow, sequential duplication to species diversity, Albert
said.
The common ancestor of coffee and such plants
as cacao, tomatoes, grapes, papaya, soybeans, strawberries, peaches and poplars
experienced no such whole-genome duplication.
"Yet the coffee family is the
fourth-largest family of flowering plants and it’s very diverse in flower,
plant and fruit form,” Albert said. “Here’s a diversification without a whole
genome duplication having stimulated it.”
The largely French team of researchers used
crushed stems, leaves and flower parts from Coffea
canephora, one of the parents of the hybrid Coffea arabica, from which
the bulk of coffee is brewed. They produced an annotated genome
that consists of 710 million building blocks.
The ensuing database is expected to boost
researchers' ability to study the highly sensitive plant behind the top
revenue-generating export of dozens of nations on four continents. About 39
countries exported 5.3 metric tons coffee of coffee beans last year, according
to the International Coffee Organization, a trade group.
A tropical perennial, coffee has a relatively
narrow temperature and rain tolerance, and its cultivation is threatened by
shifting climate patterns and by several pests. Researchers have been eager to
find ways to boost the plant's natural defenses, while others have successfully
created strains that are all but caffeine-free. Food corporations such as
Nestle have patented genetically modified coffee plants.
Genetic research and development could have
profound economic and social impacts, said Medrano of UC Davis.
Coffee crops in Central America were badly
damaged last year after a climate swing from humid to arid conditions, driving
up prices and putting about 370,000 people out of work, Medrano said.
Climate change has allowed a fungal blight to
"explode," spreading to higher altitudes where the best quality
coffee is cultivated, Medrano said. “Climate change has had a dramatic
effect on coffee," he said.
Medrano and other UC Davis researchers have
been studying how to apply DNA technology to breed coffee that is more
resistant to blight and climate fluctuations.
“There is an opportunity in the future to do
GMOs, but our interest at UC Davis is to apply plant breeding technologies to
improve the sustainability of coffee," Medrano said. "There’s a
social and cultural component to coffee. It affects the lives of so many
people.”
-----
Read the
report: The
coffee genome provides insight into the convergent evolution of caffeine biosynthesis
(pdf)
No comments:
Post a Comment
Join the conversation