Athens, Georgia, USA
January 29, 2009
By Stephanie Schupska,
University of Georgia
Southerners may best know sorghum as sweet, biscuit-topping
syrup. But the small grain’s uses range from a dependable,
drought-tolerant food crop to biofuel source, says a University
of Georgia researcher.
“Sorghum’s importance is enormous,” said Andrew Paterson, a
distinguished research professor and director of the Plant
Genome Mapping Laboratory. PGML is a joint unit of the UGA
College of Agricultural and Environmental Sciences and Franklin
College of Arts and Sciences.
Paterson and his collaborators – from as close as South Carolina
and as far away as India, Pakistan and Germany – have mapped and
analyzed the genome of Sorghum bicolor, placing 98 percent of
its genes in their chromosomal context. At 730 million bases, or
letters of DNA, sorghum has a genetic code a quarter the size of
the human genome.
The results of the study appear in the Jan. 29 issue of the
international science journal Nature.
Why is this information important?
Drought tolerance makes sorghum important in dry regions like
northeast Africa and the U.S. southern plains. It needs only
half the water it takes to grow corn.
“Not nearly as much has been invested in sorghum as in corn,”
Paterson said. “According to the United Nations Food and
Agriculture Organization, sorghum yields increased less than one
percent per year over the last 45 years, only about half the
rate of corn, rice and wheat yields. Something is wrong with
this picture. If new information and tools from the sequencing
change that, it’ll improve millions of people’s lives.”
The sorghum that Paterson studied is drought tolerant, but its
wild cousins can survive on even less water and resist more
diseases and pests. Breeders can use the sequence as a tool to
blend desirable traits into more improved commercial plants.
Biofuel potential
The sequenced sorghum genome is also being used to improve
biofuel crops like sugarcane and Miscanthus, a genus of 15
species of perennial grasses that is a leading biofuel crop in
Europe. These plants have much larger and more complicated
genomes than sorghum. A close relative, sorghum can be a guide
to accelerating their improvement.
In the U.S., it’s not clear whether Miscanthus or switchgrass
will dominate the biofuel arena, Paterson said, but recent
side-by-side studies show that Miscanthus out yields switchgrass
by as much as three to one.
Sorghum is also used to make biofuel and currently is the No. 2
source of fuel ethanol in the U.S. Corn is No. 1.
Multiple uses
Production is shifting away from seed-based biofuel to
cellulose-based production, a process for which sorghum also
shows great promise. This shifted prompted the U.S. Department
of Energy’s Joint Genome Institute’s involvement in sorghum
sequencing.
The sorghum genome sequence also has other uses. Johnson grass,
a crop related to sorghum, is one of the world’s worst weeds.
Paterson hopes that by using the sequence, researchers can find
better ways of controlling the weed.
A third use of the genome sequence will be to understand the
reasons that sorghum, rice and other cereals are different from
one another.
Sorghum is only the second grass genome sequenced. Rice was the
first. While the two grasses are similar – 93 percent of the
genes present in sorghum are also found in rice – the
differences are important enough to warrant closer inspection.
The sorghum and rice connection
For example, Paterson’s team discovered that sorghum’s seed
protein genes are completely different than rice seed protein
genes. But they don’t know how and why.
“The genes don’t just stand out and say, ‘Here I am. This is why
I’m different from rice,’” Paterson said. “We have a lot of new
questions to ask.”
He would like to continue to build on his 17 years of sorghum
research to find out what happened to sorghum and rice’s common
ancestor millions of years ago to form the plants that sustain
us today. |
|
