Submitted to: Transgenic Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2007
Publication Date: 3/27/2007
Citation: Bicar, E.H., Woodman-Clikeman, W., Sangtong, V., Peterson, J., Lee, M., Scott, M.P. 2007. Production of Transgenic Maize with Improved Amino Acid Balance Containing a Milk Protein in Grain. Transgenic Research. 11:11-20. Interpretive Summary: The majority of maize produced in the US is used for animal feed, however, maize is nutritionally deficient in the essential amino acid lysine. Meat producers therefore add synthetic lysine to corn-based animal diets, increasing the cost of feed and, therefore, increasing the cost of meat as well. Maize with increased lysine content requires less supplementation and animal feed made from this maize therefore costs less. This reduces the cost of meat production, benefiting meat producers and consumers. We developed maize with increased lysine content by introducing a synthetic gene that produces a protein that occurs naturally in milk. This protein accumulates only in the grain of the transgenic maize and not in other plant tissues. We describe the genetic inheritance of this transgene and the biochemical properties of the grain. This transgene product increases the lysine content of endosperm tissue by about 40% with little or no change to the total protein content. Demonstration of the feasibility of manipulating grain lysine content by producing a foreign protein in seeds is an important accomplishment because it provides a model system to scientists interested in manipulating grain quality using foreign proteins. We do not consider this approach commercially viable at this time because several critical issues need to be addressed before the value of this approach can be fully assessed. Foremost among these is determining the antigenic potential of this grain. Evaluation of impacts on crop marketing, seed quality and other plant characteristics and effects on animal health will be important considerations as well.
Technical Abstract: In order to meet the protein nutrition needs of the world population, greater reliance on plant protein sources will become necessary because they provide protein nutrition efficiently. The amino acid content of plant protein does not meet the requirements of monogastric animals, limiting its nutritional value. The essential amino acid lysine is deficient in cereal crops, for example. Maize is a major component of human and animal diets worldwide and especially where sources of plant protein are in critical need, such as sub-Saharan Africa. To improve the amino acid balance of maize, we developed transgenic maize lines that produce the milk protein '-lactalbumin in the endosperm. Lines in which the transgene was inherited as a single dominant genetic locus were identified. Sibling kernels with or without the transgene were compared to determine the effect of the transgene on kernel traits in lines selected for their high content of '-lactalbumin. Total protein content in endosperm from transgene positive kernels was not significantly different from total protein content in endosperm from transgene negative kernels from the same ear in three out of four comparisons, whereas the lysine content of the lines examined was 29 to 47% greater in endosperm from transgene positive kernels. This approach could be used to produce maize germplasm with a higher nutritional value and could expedite introduction of this trait into a wide variety of germplasm. Assessment of the antigenicity and impacts on animal health will be required in order to determine the overall value of this technology.