LINDELL BEACH, B.C. – Researchers have figured out what makes corn kernels hard.
It’s important because the characteristic allows corn to be easily harvested, stored and shipped.
The findings could lead to better hybrids and increase the production of a dependable supply of nutritious food for millions of people in the developing world.
The discovery focuses on a breed of corn known as quality protein maize (QPM), which incorporates two key features: a source of protein for food and a hard-shelled kernel.
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“Because it was for developing countries, (scientists at) CIMMYT (International Maize and Wheat Improvement Center), a research organization in Mexico, took the natural variations in corn and tested all the different backgrounds to see whether there was one that could be used to develop hard kernels,” said Joachim Messing, a professor of molecular genetics at Rutgers in New Jersey.
“They did find something and developed quality protein maize. That is now produced in some of the developing countries where millions of people depend on it.”
According to the CIMMYT, corn is grown on more than 238 million acres in the developing world, especially in sub-Saharan Africa and Central and South America. More than three million acres are planted to QPM varieties and hybrids.
Corn accounts for 15 to 56 percent of the total daily calories of people in about 25 of those countries.
Corn in its natural state is low in lysine and tryptophan, which are amino acids essential for making corn an adequate source of protein. Some societies supplement the crop with soybeans for human and livestock feed.
Until the development of QPM a decade ago, corn failed to meet protein requirements. A hybrid developed in the 1960s increased protein levels but was commercially unsuccessful because its softer kernels made the crop prone to spoilage and made harvest, storage and shipping difficult.
In a paper posted in the online edition ofProceedings of the National Academy of Sciences,the Rutgers scientists reported their findings about genetic coding responsible for making QPM kernels hard.
Sturdiness comes from threshold levels of a specific gene encoded by two gene copies. Their studies found that the gene generates a protein structure around starch particles that encourages strength.
“What our paper is concerned with is that we looked at what breeders had done on the molecular level and we found that there seemed to be a particular protein present in larger amounts,” said Messing, who is also director of the Waksman Institute of Microbiology.
“We wondered if maybe the protein is all that is needed to make the kernel harder.”
As part of the research, a technique was used to eliminate, or knock out, the expression of the genes they suspected were involved in QPM kernel hardness.
After eliminating the two genes responsible for producing proteins known as gamma zeins, softer kernels were noticed.
By examining both the original kernels and the softer kernels using electron microscopy, the soft kernels lacked a protein matrix interconnecting starchy components that provided structural integrity.
Nor were the structures present in the offspring of the knock-out kernels.
Messing and his team identified the gamma zeins regulated by the two genes in question as central components of the molecular structure and central to QPM’s hardness.
“While QPM was developed in the late 1990s, scientists have not had a thorough knowledge of how kernel strength could be achieved in a rational way,” said Messing.
Messing said that their findings will make it easier for breeders to improve hybrids.
“Rather than doing a physical test, they can take a little bit of a leaf and test whether a particular gene variant, or allele, is present in the offspring. It’s a DNA test and (they) have become much simpler in recent times. Breeders will no longer have to worry about quantative traits and different genes. They need just the one gene (so) future breeding becomes very simple.”
The Rutgers findings will also help scientists understand more about the evolution of seeds and their components.
