Mejoramiento de la Calidad Nutricional y Panadera del Trigo por Ingeniera Genetica

Wheat-derived products provide the basic nutrition for more than a billion of people in the world (about 40% of humankind). Humans consume more proteins from wheat than from any other source. However, the nutritional quality of wheat proteins is limited by the low content of lysine, one of the essential amino acids that we should incorporate through the diet. As part of this thesis work, we obtained transgenic wheat lines expressing the CI-2 gene from barley under the control of a promoter that is specific for endosperm. This gene has a high content of lysine, an essential amino acid in which wheat proteins are naturally deficient. These transgenic wheat lines have an improved nutritional quality because of the higher content of lysine of their proteins.

Bread-making quality of wheat is determined by the number and type of high molecular weight (HMW) subunits of glutenins. The higher the number of HMW subunits of glutenins of a particular wheat variety, the better its bread-making quality. The HMW subunits of glutenins are very polymorphic (there are many different alleles or alternative forms of genes) and some types of subunits are associated with good bread-making quality while others confer a poor quality. The two HMW subunits of glutenins associated with the best bread-making quality in wheat are 1Dx5 and 1Ax1. HMW subunits of glutenins confer elasticity to the dough because of their particular spring shape.Dough with high elasticity are ideal to make bread.

Using genetic engineering, we transformed (genetically modified) a commercially available variety of wheat to increase the number of HMW subunits of glutenins from 5 to 6 by introducing an extra HMW subunit known as 1Ax1, which caused an increase of 21% in the content of glutenin compared to the controls. In addition, we over-expressed 1Ax1 in a variety of wheat that already had this subunit by introducing extra gene copies of 1Ax1, which increased the content of 1Ax1 by 44% in this transgenic wheat variety compared to non-transgenic wheat control. Likewise, we over-expressed the HMW subunit of glutenin 1Dx5 causing an increase of 140% in the level of this subunit and a 20% increase in the total content of glutenin.

Interestingly, the over-expression of the HMW subunits of glutenins 1Ax1 or 1Dx5 in some of the transgenic wheat lines induced the inactivation of few or all of the endogenous genes that codify for HMW subunits. This phenomenon is part of a mechanism that plants use to inactivate alien genes as a protection against viruses. As expected, these silenced transgenic wheat lines had very low levels of HMW subunit of glutenin and a very poor bread-making quality. However, these lines showed exceptional good quality for making other products such as cookies, crackers, and pizza.