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Novel approaches to improving qualities of maize endosperm
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- breeding; GFP; hemoglobin; maize; zein
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thesis / dissertation description
Maize is a high yielding crop that provides a relatively high calorie source of food and feed, but focus on yield has not improved nutritional qualities. Some nutrients that are lacking in maize are iron and essential amino acids. In this dissertation some ways that genes from maize might be used to improve nutritional quality of maize are discussed, including improvement of bioavailable iron with maize globin and exploration of maize seed storage proteins. In addition, strategies to improve maize are explored, including breeding with mutations and transgenes and investigation of the effects of selection on transgenes.Maize globin was found to be as bioavailable as ferrous sulfate, both when used as a forticant added to maize flour and when expressed in maize with an endosperm specific promoter. These results indicate that maize globin could be used to biofortify maize with highly bioavailable iron. Assessment of seed storage proteins in maize inbreds, landraces, and teosintes found unique proteins in teosintes that may be moved into maize through biotechnology or breeding to improve amino acid balance. Investigation of the effects of ensiling on seed storage proteins in maize used as ruminant feed found that longer ensiling times degraded some seed storage proteins, which may make the starch more digestible, but inoculation with Lactobacillus did not have an effect.A variety of breeding methods can be used to improve qualities of maize. Maize transformed with a construct encoding green fluorescent protein controlled by a maize seed storage protein promoter was subjected to recurrent selection in order to increase transgene expression. This resulted in increased expression of the native gene with the same promoter, while unrelated traits were not changed. Backcrossing can be used to bring a mutation or transgene into a specific genetic background, while forward breeding can be used to improve characteristics of a line that carries a gene of interest.