primary prevention of coeliac disease - Associazione Italiana ...

78 GENETICALLY DETOXIFIED GRAINS
of chromosome 1 at three homologous loci, named Gli-1. However, some w-gliadin
peptides have been found to be encoded by additional dispersed genes located on the
same arm of the same set of chromosomes. Genes controlling LMW glutenin subunits
are clustered at Glu-A3, B3, and D3 loci and only the genes coding for HMW glutenin
subunits occur on the long arm of the group 1 chromosomes, at a major locus named
Glu-1. So, the multigene family nature of the wheat genes and the spread of these genes
over six different chromosomes entail a very high degree of genetic polymorphism.
By applying a Southern analysis to the common cultivar Cheyenne, Anderson et al.
found that up to 150 genes code for a-gliadin, although only half of them are expressed
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. An Italian study showed that there is a high degree of variability in the genomic
DNA between different cultivars. A genetic polymorphism at the Gli-2 locus encoding
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for a-gliadin was evident among different subspecies of Triticum aestivum .
Naturally occurring detoxified grains
This huge genetic variability let people hope to individuate a “naturally occurring”
GDG. This was the case of the nullisomic 6A-tetrasomic 6D variety of Chinese Spring
wheat, in which chromosome 6A is missing but compensated for by two extradoses of
chromosome 6D. Preliminary results were encouraging. The administration for two
weeks of 65 grams of bread made with this wheat variety did not deteriorate absorptive
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function . However, it was later proven that these variants do contain a-gliadin, coded
by B and D chromosomes, and that they are toxic, on both histological and clinical
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ground, for patients affected by CD .
More recently, the toxicity of two lines of cultivar Raeder, one lacking the Gli-A2
encoded gliadin components and the other lacking both Gli-A2 and Gli-D1 gliadin
components was tested with an organ culture system based on coeliac duodenal biopsy
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specimens . Although the Gli-A2 components were not compensated for by extradoses
of chromosomes B and D, those lines were deficient but not devoid of gliadins.
Although the toxicity of these two mutant lines was reduced compared to the original
cultivar Raeder, yet it was still present. In conclusion, all these studies show that a
naturally-occurring non-toxic line has not been found so far.
Technologies to develop genetically detoxified grains
Technologies allowing genetic plant transformation do exist. For example, a
fragment of foreign DNA cut with a restriction enzyme, and plasmid, cut open with the
same enzyme, are mixed together. DNA ligase is added to stitch the complementary
base sequences so that the recombinant plasmid contains foreign DNA that, under
appropriate conditions, is taken up by the Agrobacterium, a naturally occurring plant
pathogen. When host plant cells are exposed to Agrobacterium, plasmid DNA is
transferred into plant chromosomes. At the end of the process transgenic plants are
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regenerated from single transformed cells (Fig. 3A) . An alternative method is the
biolistic “gene gun technique”.
A suspension of thousands of tiny gold or tungsten particles coated with transgenic
DNA are fired into the target tissue, using compressed helium as propellant. Particles
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penetrate the nucleus and incorporate into the host genoma (Fig. 3B) .