High Lysine and High Tryptophan Transgenic Maize Resulting from the Reduction of Both 19- and 22-kD α-zeins

Abstract

The major maize seed storage proteins, zeins, are deficient in lysine and tryptophan content, which contribute to the poor nutritional quality of corn. Whether through the identification of mutations or genetic engineering, kernels with reduced levels of zein proteins have been shown to have increased levels of lysine and tryptophan. It has been hypothesized that these increases are due to the reduction of lysine-poor zeins and a pleiotropic increase in the lysine-rich non-zein proteins. By transforming maize with constructs expressing chimeric double-stranded RNA, kernels derived from stable transgenic plants displayed significant declines in the accumulation of both 19- and 22-kD alpha-zeins, which resulted in higher lysine and tryptophan content than previously reported for kernels with reduced zein levels. The observation that lysine and tryptophan content is correlated with the protein levels measured in transgenic maize kernels is consistent with the hypothesis that a pleiotropic increase in non-zein proteins is contributing to an improved amino acid balance. In addition, a large increase in accumulation of free amino acids, consisting predominantly of asparagine, aspartate and glutamate, was observed in the zein reduction kernels.

Nonredundant Function of Zeins and Their Correct Stoichiometric Ratio Drive Protein Body Formation in Maize Endosperm

“…Previous use of RNAi to selectively eliminate specific g-zein transcripts and a-zein subfamily transcripts have advanced our understanding of zein function and their inverse relationship to kernel protein quality (Segal et al, 2003;Huang et al, 2004Huang et al, , 2006Messing, 2010, 2011), but questions concerning their distinct roles remain unanswered. This study took advantage of RNAi technology to address the extent of functional nonredundancy within the g-and a-zein subclasses.…”

Increasing the production yield of recombinant protein in transgenic seeds by expanding the deposition space within the intracellular compartment

“…The reduced production of both the 19 and 22 kD major α-zeins results in higher non-zein protein content. 24 These studies suggest that the production yield of foreign proteins may be effectively increased by redirecting intrinsic seed protein production to foreign protein production. The production yields of foreign recombinant proteins are greatly increased by the simultaneous reduction of the expression of endogenous seed protein genes by RNA interference (anti-sense technology) or mutation.…”

Improving the Content of Essential Amino Acids in Crop Plants: Goals and Opportunities

“…Attempts have also been made to reduce the content of these storage proteins by genetic engineering, using constructs designed to reduce their expression in seeds (Segal et al, 2003;Huang et al, 2005Huang et al, , 2006. Interestingly, specific reduction of zeins by this approach also causes an opaque phenotype (Segal et al, 2003), implying that this phenotype is directly associated with the reduction of zein storage proteins.…”