Genetic Transformation of Wheat: Advances in the Transformation Method and Applications for Obtaining Lines with Improved Bread-Making Quality and Low Toxicity in Relation to Celiac Disease

Abstract

Wheat is one of the most important crops and is counted among the “big three” cereal crops (rice, wheat and maize), with an annual world production of around 680 million tonnes in 2009. Wheat is also one of the main sources of calories and proteins in the human diet. However, in spite of its global importance, wheat has been one of the last crops being transformed and it was not until 1992 when Vasil et al. (1992) obtained the first fertile transgenic plant of wheat. Nowadays, wheat transformation still presents more difficulties than transformation of other cereals, such as rice and maize, with lower transformation efficiencies and greater genotype dependence (Shewry & Jones, 2005). Particle bombardment is the most widely used method for genetic transformation of wheat, presenting higher transformation efficiencies than Agrobacterium-mediated transformation (Lazzeri & Jones, 2009). However, particle bombardment causes physical damage to the scutellar tissues used for transformation, negatively affecting the embryogenesis, in vitro regeneration of the explants and therefore the transformation efficiency. Osmotic treatment is thought to offer protection to bombarded material by minimising cytoplasm leakage from target cells (Vain et al., 1993), so it is of great importance to optimise the duration and moment of application of the osmotic treatment to the explants. Among the applications of genetic transformation, gene over-expression and posttranscriptional gene silencing (PTGS) are two strategies successfully used to enhance the wheat quality. In particular, the baking quality of wheat, largely determined by the high molecular weight glutenin subunits (HMW-GS), is one of the most important targets for genetic transformation. Transgenic wheat lines expressing additional copies of the 1Ax1, 1Dx5, 1Dy10 HMW-GS genes were obtained by particle bombardment by Leon et al. (2009) (Fig. 1 A). In addition, new lines combining the three transgenic events were obtained by conventional crossing (Leon et al., 2010) (Fig. 1 B). Therefore, a set of