Transgenic Modifications That Enhance the Utility of Seed Storage Proteins
As a preliminary evaluation of the safety of transgenic plants, the verification of substantial equivalence with the genetically unmodified counterpart is now widely employed (Kuiper et al., 2001). Modern, transcriptomic, proteomic, and metabolomic profiling techniques can be a vital part of such testing. Although substantial equivalence measurements are not safety assessments in themselves, they can reveal biochemical differences that can then be subjected to more rigorous toxicological and immunologic testing.
A potential consequence of the genetic modification of crop plants is introduction or creation of allergens. This could occur in several possible ways, including introduction of unknown allergens with the transgenic protein itself, modification by the host transgenic plant of the immunogenic properties of the transgenic protein, modification of the immunogenicity of endogenous proteins in the transgenic plant, and dissemination of an allergen through pollen that induces respiratory sensitization (Moneret-Vautrin, 2002). Such risks need to be evaluated prior to widespread use of a transgenic crop plant. Unfortunately, the possibility of allergen induction can be exaggerated to the general public and used to fuel the idea that genetic modification is an unpredictable and irresponsible science. It is true that the allergenicity of proteins, such as BNA, may not be widely known before their introduction into a crop plant. However, the scientific community quickly becomes aware of such potential problems (Nordlee et al., 1996) and acts appropriately.
Soybean consumption is a problem for some people and animals as it contains several dominant allergenic proteins: Gly m Bd 68K, Gly m Bd 28K, and Gly m Bd 30K (P34) (Ogawa et al., 2000). The widespread use of soybean in the human foods and animal feeds makes it an obvious target for genetic engineering to remove or reduce these allergens. Gly m Bd 68K and Gly m Bd 28K are seed storage proteins, and some reduction of their levels has been achieved through the development of mutant lines (Ogawa et al., 2000). However, such a strategy has not been successful with P34, which is an albumin and a member of the papain family of cysteine proteases (Ogawa et al., 2000). Although this protein is a minor seed constituent, it is the most dominant soybean allergen (Yaklich et al., 1999).
Rice induces allergic reactions in some people and this is a growing problem in some countries, like Japan (Watanabe, 1993). One of the major rice allergens was identified as a 16-kDa albumin (Matsuda et al., 1988; Urisu et al., 1991). This protein is encoded by a multigene family composed of at least ten members (Tada et al., 2003), each of which has allergenic properties (Matsuda et al., 1991).