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.