Geneticist seeks a better corn
Pork and poultry producers could one day be the beneficiaries of corn genetic research being conducted at the University of Nebraska-Lincoln. The research is being led by David Holding, a plant molecular geneticist who came to UNL in 2009 from the University of Arizona.
“My work focuses on studying the relationship between kernel texture and protein quality in corn grain,” explains Holding, an assistant professor in the UNL Department of Agronomy and Horticulture and a member of the university’s Center for Plant Science Innovation.
“Though corn grain contains a fair amount of protein, this protein is incomplete for humans and livestock because it lacks several amino acids that are essential in the diets of monogastric animals,” says Holding. “That’s why corn grain must be supplemented with different protein sources, such as soybeans, to avoid deficiency.”
At a glance
• UNL scientist studies new frontiers in corn genetics.
• One of his objectives is a higher quality of protein in corn.
• The relationship between kernel texture and protein is key.
Holding says the use of high-quality protein corn could potentially result in savings for monogastric livestock producers by reducing the amount of soybean supplementation needed in livestock. “This could allow diversion of a higher percentage of soybeans to other uses, such as biodiesel. It is also possible that these corn lines could ultimately be marketed as a value-added product, allowing the grower to command a higher price for the grain.”
As background for explaining his research, Holding points to the 1960s when a new corn variety was discovered that had a protein quality equivalent to milk. Unfortunately, this new variety, called opaque2, had soft, chalky kernels that made it unsuitable for large-scale production, storage and processing, he explains.
Corn breeders subsequently created modified versions of opaque2 that had high-quality protein and normal hard-texture grain, according to Holding. “These were termed Quality Protein Maize, or QPM. Today, QPM is being cultivated in many developing countries, where it is helping to alleviate protein malnutrition, as well as contributing to improved livestock nutrition,” he says.
Not widely used in U.S.
“Despite the obvious advantages of QPM,” says Holding, “these corn lines have not been developed for use in U.S. agriculture for several reasons, including the complicated and largely unknown underlying genetics of the QPM trait.” Also, he adds, “maintaining the recessive mutant opaque2 gene is problematic for breeding.”
Another big reason for limited development of QPM corn varieties in the United States has been relatively low costs of corn and soybeans for use in livestock feeds.
Holding’s laboratory is identifying specific genes that control the process of protein quality and kernel hardness. “We are studying their function at the cellular level and designing ways to use them to create high-yielding, hard-kernel corn lines that have the value-added trait of high-quality protein,” he explains. “We are exploring the development of such lines using both breeding and biotechnological approaches.”
Several genes and their encoded proteins are believed to be involved in converting soft grain opaque2 into QPM. For example, genetic and biochemical analysis has previously implicated one major protein, called gamma zein, as being important, says Holding. “By identifying and functionally characterizing other genes involved, we will understand how QPM develops and be able to optimize corn for both hard kernel texture and high-quality protein.”
A recent discovery in Holding’s laboratory has shown that opaque2 kernels undergo cellular stresses that use a substantial amount of cellular energy resources and may contribute to the soft kernel texture. “These stresses do not occur in QPM kernels, and we are investigating the role of a ‘master protein’ in QPM that seems to provide a switch in ‘energy currency’ to alleviate these stresses.”
Corn has a tremendous amount of diversity in terms of its size and adaptation to growth in different climates, latitudes and altitudes, Holding says. “This is reflected in extreme genetic variation, so we are surveying many different corn genetic backgrounds for novel QPM genes. We are also conducting a large-scale gene mutagenesis approach in QPM to knock out and then map and identify QPM genes.”
Holding is convinced that, along with research to improve the yield and resilience of grain crops, it is essential that scientists also focus on improving nutritional quality for the improved feeding efficiencies that this would bring.
He acknowledges he is still in the early stages of research for creating biotechnologically developed corn lines. “The possible benefits for agriculture are real, but they are not immediate,” he concludes.
Carlton writes from Lincoln.