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2-Plants: Enriched lysine plants to fight malnutrition

-------------------------------- GENET-news -------------------------------

TITLE:  Enriched lysine plants to fight malnutrition
SOURCE: Checkbiotech, Switzerland, by Shelley Jambresic
DATE:   11 Aug 2005

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Enriched lysine plants to fight malnutrition

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

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


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