The main nutritional limitation of maize used for feed is the content of protein that is digestible, bioavailable and contains an amino acid balance that matches the requirements of animals. In contrast, milk protein has good digestibility, bioavailability and amino acid balance. As an initial effort to create maize optimized as a source of swine nutrition, a codon-adjusted version of a gene encoding the milk protein porcine alpha-lactalbumin was synthesized. Maize expression vectors containing this gene under the control of the Ubi-1 promoter and nos 3' terminator were constructed. These vectors were used to transform maize callus lines that were regenerated into fertile plants. The alpha-lactalbumin transgenes were transmitted through meiosis to the sexual progeny of the regenerated plants. Porcine alpha-lactalbumin was detected in callus and kernels from transgenic maize lines that were transformed by two constructs containing the 27-kDa maize gamma-zein signal sequence at the 5' end of the synthetic porcine alpha-lactalbumin coding sequence. One of these constructs contained an ER retention signal and the other did not. Expression was not observed in kernels or callus from transgenic maize lines that were transformed by a construct that does not contain an exogenous protein-targeting signal. This suggests that the signal peptide might play an important role in porcine alpha-lactalbumin accumulation in transgenic maize kernels.

Mutations in the Opaque2 (O2) gene of maize (Zea mays L.) improve the nutritional value of maize by reducing the level of zeins in the kernel. The phenotype of o2 grain is controlled by many modifier genes and is therefore strongly dependent on genetic background. We propose two hypotheses to explain differences in phenotypic severity in different genetic backgrounds: (i) Specific genes are differentially (o2 vs. wild‐type) expressed only in certain genotypes, and (ii) A set of genes are differentially expressed in all backgrounds, but the degree of differential expression differs in different backgrounds. To determine the extent to which these two hypotheses contribute to determining the severity of o2 in different genetic backgrounds, we identified transcripts likely to be differentially expressed in several genetic backgrounds by transcript profile comparison of endosperm RNA pools from eight o2 inbred lines and their wild‐type counterparts. The inbred line B46 was identified as having severe o2 phenotypes while the line M14 was identified as having minimal o2 phenotypes. The degree of wild‐type vs. o2 differential expression of transcripts was determined for these two lines. We found that most genes that are downregulated by o2 tend to be differentially expressed to a greater degree in B46 than in M14, while upregulated genes tend to be more highly differentially expressed in one genetic background or the other. Thus, hypothesis one functions more prominently for upregulated genes while hypothesis two functions most prominently for downregulated genes.

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