By Shelley Jambresic, Checkbiotech

One billion people worldwide are suffering from malnutrition. Due to the high demand for energy and essential nutrients, infants and children are at particular risk of undernutrition, but supplemented plants may offer a solution. In a recent review in the Brazilian Journal of Medical and Biological Research, Doctors Renato Rodriguez Ferreira, Vanderlei Aparecido Varisi, Lyndel Wayne Meinhardt, Peter John Lea and Ricardo Antunes Azevedo took a closer look at the production of high-lysine crops.

About one third of the world's children are affected by symptoms of protein and vitamin malnutrition such as: developmental and growth retardation, increased risk of infection and higher risk of death and blindness. Therefore, one of the challenges has been the production of crops containing higher concentrations of essential amino acids, such as lysine. However, apart from protein enriched maize currently commercially available, the release of high-protein crops has not yet occurred.

The quest for protein enriched crops arises with the problem that humans cannot synthesize all amino acids on their own, and therefore must obtain some from their diet. Humans need nine essential amino acids, such as lysine, methionine, threonine or isoleucine that they cannot produce on their own.

The amount of essential amino acids, along with how well a protein can be digested, determine its nutritional quality for humans.

"Lysine is one of the most limiting amino acids in plants consumed by humans," explained Dr. Azevedo from Departamento de Genetica in Sao Paulo, Brazil in the Brazilian Journal of Medical and Biological Research. In western societies, meat is the main source of essential amino acids such as lysine.

"However, in developing countries the main, and sometimes only source, are plants," Dr. Azevedo further said.

In addition, in many developing countries, these plants that Dr. Azevedo referred to constitute practically the entire diet of an average person. Compounding the problem is that the grains from these plants lack lysine, which causes malnutrition symptoms.

In order to decrease the problem of malnutrition, various studies have been carried out to obtain a better understanding of the biosynthesis of lysine. The overall aim in the end was to be able to construct genetically engineered plants producing higher amounts of lysine in their seeds.

Several strategies have been developed for the production of high-lysine plants. The conventional, long-term plant breeding programs – a simple and traditional, but effective approach - have been used to select plants with improved protein quality. Perhaps the most significant finding through this approach was the naturally occurring high-lysine maize mutant, opaque-2. However, field studies eventually showed that these high-lysine maize varieties were not productive enough for agricultural uses.

"The correlation between nutritional quality and yield has been a serious issue over the years, since the two factors appear to be negatively correlated," Dr. Azevedo told the Brazilian Journal of Medical and Biological Research. "Unfortunately, the high-lysine mutants exhibited undesirable agronomic characteristics."

Only more recently, in 1999 Gaziola et al. partially overcame the negative traits with the development of a genetically engineered quality protein maize. "These new maize hybrids have been designated QPM (quality protein maize) and several hybrids were produced and introduced into the market", said Dr. Azevedo. "However, the widespread use of these varieties has not been as fast as initially expected."

Despite the better agronomical quality, research led by Dr. Azevedo’s laboratory described in 2001 that the engineering of the lysine biosynthesis in plants did not lead to lysine production in the seeds, rather in the leaves. Furthermore, the modified genes also showed to have an effect on the biosynthesis of other amino acids and enzymatic activities.

Various studies with lysine producing plants include the production of alternative maize mutants, as well as other important cereal crops such as rice, barely and sorghum. Such high-lysine plants could be more useful in terms of commercial use, while also decreasing the incidence of malnutrition and undernutrition in developing countries.

"In 1997, when reviewing the aspartate metabolic pathway, we hoped that in five years high-lysine transgenic crop plants would be available to farmers," explained Dr. Azevedo.

Still, apart from the QPM lines, very little else in the way of high-lysine crops is available nowadays. Dr. Azevedo suggested in the Brazilian Journal of Medical and Biological Research, "Perhaps recent legislations and general concern about the use of modified genetic organisms have been the major setback regarding the release of such crops."

Ferreira et al. Are high-lysine cereal crops still a challenge? Brazilian Journal of Medical and Biological Research. 2005